Summary of Significant Accounting Policies (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Earnings Per Share
Preferred stock, shares outstanding	12,050		12,050		12,275
Net income loss available to common stockholders
Net income	$ (12,180,000)	$ 66,667,000	$ 53,091,000	$ 145,286,000
Net income applicable to preferred stock		12,914,000	9,983,000	28,183,000
Net income applicable to common stock		53,753,000	43,108,000	117,103,000
Determination of shares:
Weighted-average common shares outstanding (in shares)	78,306,436	76,257,000	77,932,000	76,126,000
Assumed conversion of dilutive employee stock-based awards (in shares)		2,453,000	3,058,000	2,325,000
Assumed conversion of restricted stock (in shares)		142,000	92,000	146,000
Assumed conversion of preferred stock (in shares)		27,278,000	22,850,000	27,278,000
Diluted weighted-average common shares outstanding (in shares)		106,130,000	103,932,000	105,875,000
Anti-dilutive securities, options to purchase shares outstanding	10,638,637	1,700,528	99,625	3,125,403
Calculation of basic EPS:
Net income applicable to common stock		53,753,000	43,108,000	117,103,000
Weighted-average common shares outstanding (in shares)	78,306,436	76,257,000	77,932,000	76,126,000
Basic earnings per common share	$ (0.16)	$ 0.70	$ 0.55	$ 1.54
Calculation of diluted EPS:
Net income	(12,180,000)	66,667,000	53,091,000	145,286,000
Diluted weighted-average common shares outstanding (in shares)		106,130,000	103,932,000	105,875,000
Diluted earnings per common share	$ (0.16)	$ 0.63	$ 0.51	$ 1.37
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			26,777,778
Common stock price between $45 and $67
Determination of shares:
Aggregate liquidation preference of preferred stock	$ 1,205,000,000		$ 1,205,000,000
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			26,777,778
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			17,985,075
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			17,985,075