Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Net income loss available to common stockholders
Net income	$ 5,104	$ 23,708
Net income applicable to preferred stock		2,282
Net income applicable to common stock	$ 5,104	$ 21,426
Determination of shares:
Weighted-average common shares outstanding (in shares)	90,751,000	80,968,000
Assumed conversion of dilutive employee stock-based awards (in shares)	1,105,000	1,448,000
Assumed conversion of restricted stock (in shares)	61,000	51,000
Diluted weighted-average common shares outstanding before participating security	91,917,000	82,467,000
Assumed conversion of preferred stock (in shares)		8,624,000
Diluted weighted-average common shares outstanding (in shares)	91,917,000	91,091,000
Calculation of basic EPS:
Net income applicable to common stock	$ 5,104	$ 21,426
Weighted-average common shares outstanding (in shares)	90,751,000	80,968,000
Basic EPS (in dollars per share)	$ 0.06	$ 0.26
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 5,104	$ 21,426
Diluted weighted-average common shares outstanding before participating security	91,917,000	82,467,000
Diluted EPS (in dollars per share)	$ 0.06	$ 0.26
Anti-dilutive securities, options to purchase shares outstanding	4,545,585	2,574,719
Series C Preferred Stock
Earnings Per Share
Preferred stock, shares outstanding	0	8,624	0