Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Net income loss available to common stockholders
Net income	$ 789,340	$ 46,535	$ 811,523	$ 104,278
Net income applicable to preferred stock		3,658		9,268
Net income applicable to common stock	$ 789,340	$ 42,877	$ 811,523	$ 95,010
Determination of shares:
Weighted-average common shares outstanding (in shares)	90,913,000	83,065,000	90,865,000	81,917,000
Assumed conversion of dilutive employee stock-based awards (in shares)	2,582,000	1,233,000	1,957,000	1,381,000
Assumed conversion of restricted stock (in shares)	94,000	38,000	81,000	41,000
Diluted weighted-average common shares outstanding before participating security	93,589,000	84,336,000	92,903,000	83,339,000
Assumed conversion of preferred stock (in shares)		7,086,000		7,991,000
Diluted weighted-average common shares outstanding (in shares)	93,589,000	91,422,000	92,903,000	91,330,000
Calculation of basic EPS:
Net income applicable to common stock	$ 789,340	$ 42,877	$ 811,523	$ 95,010
Weighted-average common shares outstanding (in shares)	90,913,000	83,065,000	90,865,000	81,917,000
Basic EPS (in dollars per share)	$ 8.68	$ 0.52	$ 8.93	$ 1.16
Calculation of diluted EPS using two class method:
Net income applicable to common stock	$ 789,340	$ 42,877	$ 811,523	$ 95,010
Diluted weighted-average common shares outstanding before participating security	93,589,000	84,336,000	92,903,000	83,339,000
Diluted EPS (in dollars per share)	$ 8.43	$ 0.51	$ 8.74	$ 1.14
Anti-dilutive securities, options to purchase shares outstanding	36,934	3,155,496	87,160	2,990,243
Series C Preferred Stock
Earnings Per Share
Preferred stock, shares outstanding	0	6,931	0	6,931	0