| Consolidated Statement of Changes in Stockholders' Equity (USD $) | Total
 USD ($) | Class B Common Stock | Class A Common Stock | Preferred Stock
 USD ($) | Common Stock
 Class B Common Stock
 USD ($) | Common Stock
 Class A Common Stock
 USD ($) | Additional Paid-in Capital
 USD ($) | Retained Earnings
 USD ($) | Treasury Stock
 USD ($) | Minority Interest
 USD ($) | Accumulated Other Comprehensive Income (Loss)
 USD ($) | 
|---|---|---|---|---|---|---|---|---|---|---|---|
| Balance at Dec. 31, 2011 | $ 236,421,035 | $ 0 | $ 1,800 | $ 3,071 | $ 86,067,852 | $ 161,335,621 | $ (9,182,571) | $ 63,614 | $ (1,868,352) | ||
| Treasury Stock, Shares at Dec. 31, 2011 | 4,833,284 | 4,833,284 | |||||||||
| Common Stock, Shares, Outstanding at Dec. 31, 2011 | 18,000,000 | 25,880,553 | 18,000,000 | 30,713,837 | |||||||
| Preferred Stock, Shares, Outstanding at Dec. 31, 2011 | 0 | 0 | |||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||
| Exercise of stock options (in shares) | 1,151,327 | 1,151,327 | |||||||||
| Exercise of stock options | 3,016,256 | 115 | 3,016,141 | ||||||||
| Stock-based compensation expense, including excess tax benefits of $2,375,223 | 4,903,149 | 4,903,149 | |||||||||
| Changes in minority interest in foreign subsidiary | 7,700 | 7,700 | |||||||||
| Foreign currency translation adjustment | 957,808 | 957,808 | |||||||||
| Unrealized gain from interest rate hedge, net of tax | 297,950 | 297,950 | |||||||||
| Net income | 13,445,348 | 13,445,348 | |||||||||
| Balance at Sep. 30, 2012 | $ 259,049,246 | $ 0 | $ 1,800 | $ 3,186 | $ 93,987,142 | $ 174,780,969 | $ (9,182,571) | $ 71,314 | $ (612,594) | ||
| Preferred Stock, Shares, Outstanding at Sep. 30, 2012 | 0 | 0 | |||||||||
| Treasury Stock, Shares at Sep. 30, 2012 | 4,833,284 | 4,833,284 | |||||||||
| Common Stock, Shares, Outstanding at Sep. 30, 2012 | 18,000,000 | 27,031,880 | 18,000,000 | 31,865,164 | 
| X | ||||||||||
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- Definition Minority interest in foreign subsidiary No definition available. 
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- Definition This element represents the amount of recognized equity-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Alternate captions include the words "stock-based compensation". Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Details 
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| X | ||||||||||
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Net of tax and reclassification adjustments of the change in the balance sheet adjustment that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency of the reporting entity. Also includes the following: gain (loss) on foreign currency forward exchange contracts; foreign currency transactions designated as hedges of net investment in a foreign entity and intercompany foreign currency transactions that are of a long-term nature, when the entities to the transaction are consolidated, combined, or accounted for by the equity method in the reporting enterprise's financial statements; and gain (loss) on a derivative instrument or nonderivative financial instrument that may give rise to a foreign currency transaction gain (loss) that has been designated and qualified as a hedging instrument for hedging of the foreign currency exposure of a net investment in a foreign operation. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Net of tax amount, before reclassification adjustments, of the change in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Also includes an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Number of share options (or share units) exercised during the current period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Value of stock issued as a result of the exercise of stock options. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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