Summary of Significant Accounting Policies (Details 5) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share
Preferred stock, shares outstanding	12,275				12,275				12,275	12,275
Net income loss available to common stockholders
Net income	$ 20,239,000	$ 46,446,000	$ 66,667,000	$ 78,619,000	$ 44,031,000	$ 70,803,000	$ 75,989,000	$ 51,528,000	$ 211,971,000	$ 242,351,000	$ (59,467,000)
Net income applicable to preferred stock									41,023,000	46,101,000
Net income applicable to common stock									170,948,000	196,250,000
Determination of shares:
Weighted-average common shares outstanding (in shares)									76,345,000	77,991,000	78,078,602
Assumed conversion of dilutive employee stock-based awards (in shares)									2,464,000	1,782,000
Assumed conversion of preferred stock (in shares)									24,995,000	27,278,000
Diluted weighted-average common shares outstanding (in shares)									103,804,000	107,051,000
Calculation of basic EPS:
Net income applicable to common stock									170,948,000	196,250,000
Weighted-average common shares outstanding (in shares)									76,345,000	77,991,000	78,078,602
Basic earnings per common share	$ 0.21	$ 0.49	$ 0.70	$ 0.83	$ 0.46	$ 0.73	$ 0.79	$ 0.53	$ 2.24	$ 2.52	$ (0.76)
Calculation of diluted EPS:
Net income (loss)	20,239,000	46,446,000	66,667,000	78,619,000	44,031,000	70,803,000	75,989,000	51,528,000	211,971,000	242,351,000	(59,467,000)
Diluted weighted-average common shares outstanding (in shares)									103,804,000	107,051,000
Diluted earnings per common share	$ 0.19	$ 0.44	$ 0.63	$ 0.74	$ 0.41	$ 0.66	$ 0.71	$ 0.48	$ 2.04	$ 2.26	$ (0.76)
Anti-dilutive securities, options to purchase shares outstanding									1,693,500	3,004,402	10,834,444
Common stock price less than $45
Determination of shares:
Common stock price (in dollars per share)	$ 45								$ 45
Increase in diluted weighted-average common shares outstanding									27,277,778
Common stock price between $45 and $67
Determination of shares:
Aggregate liquidation preference of preferred stock	$ 1,230,000,000								$ 1,230,000,000
Common stock price between $45 and $67 | Maximum
Determination of shares:
Common stock price (in dollars per share)	$ 67								$ 67
Increase in diluted weighted-average common shares outstanding									27,277,778
Common stock price between $45 and $67 | Minimum
Determination of shares:
Common stock price (in dollars per share)	$ 45								$ 45
Increase in diluted weighted-average common shares outstanding									18,320,896
Common stock price more than $67
Determination of shares:
Common stock price (in dollars per share)	$ 67								$ 67
Increase in diluted weighted-average common shares outstanding									18,320,896