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Stock Incentive Plan - Narrative (Details) (USD $)
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12 Months Ended | 0 Months Ended | 12 Months Ended | 32 Months Ended | 9 Months Ended | 12 Months Ended | ||||||||||||||||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Dec. 31, 2009
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Aug. 25, 2010
Class A Common Stock
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Jul. 27, 2010
Class A Common Stock
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Dec. 31, 2012
Class A Common Stock
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Dec. 31, 2011
Class A Common Stock
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Dec. 31, 2010
2000 Plan
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Dec. 31, 2012
2010 Plan
Class A Common Stock
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Dec. 31, 2012
2010 Plan
Class A Common Stock
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Dec. 31, 2010
2010 Plan
Class A Common Stock
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Sep. 30, 2012
Stock Options
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Dec. 31, 2012
Stock Options
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Dec. 31, 2011
Stock Options
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Dec. 31, 2010
Stock Options
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Dec. 31, 2012
Stock Options
2010 Plan
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||||||||||||
| Shares reserved for future issuance | 28,500,000 | 10,000,000 | ||||||||||||||||||||
| Common stock, par value (in dollars per share) | $ 0.0001 | $ 0.0001 | $ 0.0001 | $ 0.0001 | ||||||||||||||||||
| Granted | 706,644 | [1] | 257,500 | [1] | 856,000 | 964,144 | ||||||||||||||||
| Granted (in usd per share) | $ 12.520 | [1] | $ 13.045 | $ 11.782 | [1] | |||||||||||||||||
| Stock issued during period | 342,889 | 8,696,820 | ||||||||||||||||||||
| Options vesting period | 5 years | |||||||||||||||||||||
| Price per share (in dollars per share) | $ 10.00 | $ 10.00 | ||||||||||||||||||||
| Weighted-average remaining contractual life of all options expected to vest | 8 years 3 months 26 days | |||||||||||||||||||||
| Total intrinsic value of options exercised | $ 12,829,917 | $ 31,757,430 | $ 19,947,860 | |||||||||||||||||||
| Exercise of stock options (in shares) | 1,306,145 | 2,790,188 | 1,801,906 | |||||||||||||||||||
| Exercised (in usd per share) | $ 2.651 | $ 2.305 | $ 1.484 | |||||||||||||||||||
| Proceeds from stock options exercised | 3,462,679 | 6,407,804 | 2,674,764 | |||||||||||||||||||
| Proceeds from exercises of options, warrants and issuance of stock | (3,462,679) | (6,407,804) | (60,073,139) | |||||||||||||||||||
| Expiration period | 10 years | |||||||||||||||||||||
| Share-based compensation vesting percentage | 20.00% | |||||||||||||||||||||
| Ratable vesting percentage | 5.00% | |||||||||||||||||||||
| Exercise term upon termination | 90 days | |||||||||||||||||||||
| Weighted average exercise price (in usd per share) | $ 6.794 | $ 5.151 | $ 4.177 | $ 2.680 | $ 4.03 | $ 5.59 | $ 7.57 | |||||||||||||||
| Stock-based compensation expense | 3,351,142 | 2,865,706 | 2,498,660 | 3,351,142 | 2,865,706 | 2,498,660 | ||||||||||||||||
| Non-vested stock options unrecognized compensation expense | $ 6,718,399 | |||||||||||||||||||||
| Non-vested stock options unrecognized compensation expense, weighted-average period of recognition | 3 years 2 months 1 day | |||||||||||||||||||||
| Shares available for grant | 9,049,574 | |||||||||||||||||||||
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