Summary Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 264,537	$ 495,834	$ 405,151	$ 212,290	$ 271,959	$ 538,389	$ 411,292	$ 238,610	$ 1,377,812	$ 1,460,250	$ 1,423,752
Operating (loss) income	(22,497)	161,915	80,587	(59,408)	505	205,594	27,647	(35,873)	160,597	197,873	222,716
Net (loss) income	$ (25,446)	$ 87,176	$ 37,406	$ (49,217)	$ (12,969)	$ 120,740	$ (15,900)	$ (39,951)	$ 49,919	$ 51,920	$ 74,221
(Loss) earnings per share:
Net (loss) income per share, basic	$ (0.29)	$ 1.01	$ 0.43	$ (0.56)	$ (0.14)	$ 1.35	$ (0.18)	$ (0.48)	$ 0.57	$ 0.59	$ 0.90
Net (loss) income per share, diluted	$ (0.29)	$ 1.00	$ 0.43	$ (0.56)	$ (0.14)	$ 1.34	$ (0.18)	$ (0.48)	$ 0.57	$ 0.59	$ 0.89