| Income Taxes - Unrecognized tax benefits (Details) (USD $) | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2012 | Dec. 31, 2011 | |
| Income Tax Disclosure [Abstract] | ||
| Balance, beginning of year | $ 1,400,000 | $ 8,100,000 | 
| Additions for prior year tax positions | 3,500,000 | 100,000 | 
| Settlements paid to tax authorities | 0 | 0 | 
| Reductions of prior year tax positions | 0 | (6,800,000) | 
| Balance, end of year | $ 4,900,000 | $ 1,400,000 | 
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- Details 
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- Definition The gross amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The gross amount of decreases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The gross amount of increases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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