Summary of Significant Accounting Policies - Basic and Diluted Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income (loss)	$ (544,996)	$ (1,903)	$ (758,566)	$ 1,160
Income allocable to unvested stock grants		(151)		(444)
Basic net income (loss) attributable to common stock	(544,996)	(2,054)	(758,566)	716
Diluted net income (loss) attributable to common stock	$ (544,996)	$ (2,054)	$ (758,566)	$ 716
Basic net income (loss) attributable to common stock, Shares	46,150	46,651	46,100	46,628
Effect of dilutive securities: Performance share units, Shares				320
Diluted net income (loss) attributable to common stock, Shares	46,150	46,651	46,100	46,948
Basic net income (loss) attributable to common stock, Per Share	$ (11.81)	$ (0.04)	$ (16.45)	$ 0.02
Diluted net income (loss) attributable to common stock, Per Share	$ (11.81)	$ (0.04)	$ (16.45)	$ 0.02