Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income (loss)	$ (3,746)	$ 9,761	$ 14,165	$ 51,792
Weighted average shares outstanding - basic	25,463,994	25,137,531	25,452,991	25,126,684
Net income (loss) per share	$ (0.15)	$ 0.39	$ 0.56	$ 2.06
Weighted average shares outstanding - diluted	25,704,931	25,334,716	25,684,931	25,323,187
Net income (loss) per share	$ (0.15)	$ 0.39	$ 0.55	$ 2.05