Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Earnings Per Share
Conversion of preferred stock (in shares)	516,000		1,693,000
Net income loss available to common stockholders
Net income	$ 46,535	$ 4,900	$ 104,278	$ 9,752
Net income applicable to preferred stock	3,658	476	9,268	951
Net income applicable to common stock	$ 42,877	$ 4,424	$ 95,010	$ 8,801
Determination of shares:
Weighted-average common shares outstanding (in shares)	83,065,000	80,243,000	81,917,000	79,803,000
Assumed conversion of dilutive employee stock-based awards (in shares)	1,233,000	2,355,000	1,381,000	2,307,000
Assumed conversion of restricted stock (in shares)	38,000	58,000	41,000	60,000
Diluted weighted-average common shares outstanding before participating security	84,336,000	82,656,000	83,339,000	82,170,000
Assumed conversion of preferred stock (in shares)	7,086,000	8,624,000	7,991,000	8,624,000
Diluted weighted-average common shares outstanding (in shares)	91,422,000	91,280,000	91,330,000	90,794,000
Calculation of basic EPS:
Net income applicable to common stock	$ 42,877	$ 4,424	$ 95,010	$ 8,801
Weighted-average common shares outstanding (in shares)	83,065,000	80,243,000	81,917,000	79,803,000
Basic EPS (in dollars per share)	$ 0.52	$ 0.06	$ 1.16	$ 0.11
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 42,877	$ 4,424	$ 95,010	$ 8,801
Diluted weighted-average common shares outstanding before participating security	84,336,000	82,656,000	83,339,000	82,170,000
Diluted EPS (in dollars per share)	$ 0.51	$ 0.05	$ 1.14	$ 0.11
Anti-dilutive securities, options to purchase shares outstanding			2,990,243	1,621,219
Series C Preferred Stock
Earnings Per Share
Preferred stock, shares outstanding	6,931	8,624	6,931	8,624	8,624
Shares converted (in shares)	516		1,693