Net Income per Share - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income	$ 52,591	$ 119,717	$ 322,597	$ 357,890
Denominator:
Weighted average number of shares outstanding—basic (in shares)	52,707	52,777	52,916	52,727
Dilutive restrictive stock awards	1	0	29	0
Weighted average number of shares outstanding—diluted (in shares)	52,708	52,777	52,945	52,727
Net income per share—basic (in dollars per share)	$ 1.00	$ 2.27	$ 6.10	$ 6.79
Net income per share—diluted (in dollars per share)	$ 1.00	$ 2.27	$ 6.09	$ 6.79