Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income loss available to common stockholders
Net income (loss)	$ (338,060)	$ 789,340	$ 17,079	$ 5,104	$ 5,032	$ 46,535	$ 34,035	$ 23,708	$ 473,463	$ 109,310	$ 686
Net income applicable to preferred stock										8,662	67
Net income applicable to common stock									$ 473,463	$ 100,648	$ 619
Determination of shares:
Weighted-average common shares outstanding (in shares)									90,854,000	82,929,000	80,003,000
Assumed conversion of dilutive employee stock-based awards (in shares)									2,431,000	1,299,000	2,217,000
Assumed conversion of restricted stock (in shares)									93,000	42,000	60,000
Diluted weighted-average common shares outstanding before participating security									93,378,000	84,270,000	82,280,000
Assumed conversion of preferred stock (in shares)										7,137,000	8,624,000
Diluted weighted-average common shares outstanding (in shares)									93,378,000	91,407,000	90,904,000
Calculation of basic EPS:
Net income applicable to common stock									$ 473,463	$ 100,648	$ 619
Weighted-average common shares outstanding (in shares)									90,854,000	82,929,000	80,003,000
Basic EPS (in dollars per share)	$ (3.72)	$ 8.68	$ 0.19	$ 0.06	$ 0.06	$ 0.52	$ 0.38	$ 0.26	$ 5.21	$ 1.21	$ 0.01
Calculation of diluted EPS using two class method:
Net income applicable to common stock									$ 473,463	$ 100,648	$ 619
Diluted weighted-average common shares outstanding before participating security									93,378,000	84,270,000	82,280,000
Diluted EPS (in dollars per share)	$ (3.72)	$ 8.43	$ 0.18	$ 0.06	$ 0.05	$ 0.51	$ 0.37	$ 0.26	$ 5.07	$ 1.19	$ 0.01
Anti-dilutive securities, options to purchase shares outstanding									51,803	3,036,819	1,635,929
Series C Preferred Stock
Earnings Per Share
Number of shares converted										8,624
Preferred stock, shares outstanding	0				0				0	0
Conversion of preferred stock (in shares)										8,624,000