Quarterly Operating Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information
Revenues	$ 56,768	$ 75,807	$ 73,752	$ 73,747	$ 167,798	$ 155,402	$ 176,561	$ 148,564	$ 279,574	$ 648,325	$ 667,398
Gross loss	(15,228)	(4,597)	(10,302)	(25,998)	41,118	42,150	53,648	44,364	(56,125)	181,280	192,995
Net income	$ (50,040)	$ (13,898)	$ (17,004)	$ (28,602)	$ 399	$ 13,744	$ 23,017	$ 18,427	$ (109,544)	$ 55,588	$ 84,886
Earnings (loss) per share:
Basic	$ (2.17)	$ (0.60)	$ (0.74)	$ (1.24)	$ 0.02	$ 0.60	$ 1.00	$ 0.80	$ (4.76)	$ 2.41	$ 3.67
Diluted	$ (2.17)	$ (0.60)	$ (0.74)	$ (1.24)	$ 0.02	$ 0.60	$ 1.00	$ 0.80	$ (4.76)	$ 2.41	$ 3.67