Earnings Per Share - Schedule of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic:
Net income (loss), basic	$ 11,494	$ (73,163)	$ 38,341	$ (118,697)
Basic	262,423	223,013	261,768	222,898
Basic	$ 0.04	$ (0.33)	$ 0.15	$ (0.53)
Weighted-average number of shares of common stock-diluted:
Restricted stock and performance unit awards	1,997		2,553
Diluted:
Net income (loss), diluted	$ 11,494	$ (73,163)	$ 38,341	$ (118,697)
Net income (loss), shares, diluted	264,420	223,013	264,321	222,898
Diluted	$ 0.04	$ (0.33)	$ 0.15	$ (0.53)