Earnings (Loss) per Share - Table Illustrating Computation of Basic and Diluted Earnings (Loss) Per Common Share (Detail) (USD $) In Thousands, except 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
Earnings Per Share [Abstract]
Net income (loss)	$ (63,830)	$ (46,807)	$ 15,010	$ (21,605)	$ (22,197)	$ 251	$ (24,668)	$ (17,589)	$ (117,232)	$ (64,203)	$ 110,038
Weighted average common stock outstanding
Basic	34,056,413	34,056,359	34,056,359	34,052,875	34,480,849	35,443,820	35,474,001	35,539,413	34,055,513	35,232,194	36,567,684
Diluted	34,056,413	34,056,359	35,177,915	34,052,875	34,480,849	37,484,601	35,474,001	35,539,413	34,055,513	35,232,194	37,533,391
Earnings (loss) per share
Basic	$ (1.87)	$ (1.37)	$ 0.44	$ (0.63)	$ (0.64)	$ 0.01	$ (0.70)	$ (0.49)	$ (3.44)	$ (1.82)	$ 3.01
Diluted	$ (1.87)	$ (1.37)	$ 0.43	$ (0.63)	$ (0.64)	$ 0.01	$ (0.70)	$ (0.49)	$ (3.44)	$ (1.82)	$ 2.93