Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Earnings Per Share
Conversion of preferred stock (in shares)	1,177,000
Net income loss available to common stockholders
Net income	$ 34,035	$ 2,983	$ 57,743	$ 4,852
Net income applicable to preferred stock	3,151	291	5,452	474
Net income applicable to common stock	$ 30,884	$ 2,692	$ 52,291	$ 4,378
Determination of shares:
Weighted-average common shares outstanding (in shares)	81,647,000	79,758,000	81,308,000	79,580,000
Assumed conversion of dilutive employee stock-based awards (in shares)	1,474,000	2,298,000	1,459,000	2,301,000
Assumed conversion of restricted stock (in shares)	34,000	49,000	42,000	60,000
Diluted weighted-average common shares outstanding before participating security	83,155,000	82,105,000	82,809,000	81,941,000
Assumed conversion of preferred stock (in shares)	8,331,000	8,624,000	8,478,000	8,624,000
Diluted weighted-average common shares outstanding (in shares)	91,486,000	90,729,000	91,287,000	90,565,000
Calculation of basic EPS:
Net income applicable to common stock	$ 30,884	$ 2,692	$ 52,291	$ 4,378
Weighted-average common shares outstanding (in shares)	81,647,000	79,758,000	81,308,000	79,580,000
Basic EPS (in dollars per share)	$ 0.38	$ 0.03	$ 0.64	$ 0.06
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 30,884	$ 2,692	$ 52,291	$ 4,378
Diluted weighted-average common shares outstanding before participating security	83,155,000	82,105,000	82,809,000	81,941,000
Diluted EPS (in dollars per share)	$ 0.37	$ 0.03	$ 0.63	$ 0.05
Anti-dilutive securities, options to purchase shares outstanding			2,889,501	1,604,583
Series C Preferred Stock
Earnings Per Share
Preferred stock, shares outstanding	7,447	8,624	7,447	8,624	8,624
Shares converted (in shares)	1,177