Computation of Basic and Diluted (Loss) Earnings per Share under Two-Class Method (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
Numerator for basic and diluted (loss) earnings per share:
Net (loss) income	$ (50,040)	$ (13,898)	$ (17,004)	$ (28,602)	$ 399	$ 13,744	$ 23,017	$ 18,427	$ (109,544)	$ 55,588	$ 84,886
Effect of reallocating undistributed earnings of participating securities										(376)	(530)
Net (loss) income available under the two-class method									$ (109,544)	$ 55,212	$ 84,356
Denominator:
Denominator for basic (loss) earnings per share-weighted-average shares									22,999,318	22,946,395	22,957,013
Effect of dilutive potential common shares									0	0	0
Denominator for diluted (loss) earnings per share-adjusted weighted-average shares									22,999,318	22,946,395	22,957,013
Basic (loss) earnings per share	$ (2.17)	$ (0.60)	$ (0.74)	$ (1.24)	$ 0.02	$ 0.60	$ 1.00	$ 0.80	$ (4.76)	$ 2.41	$ 3.67
Diluted (loss) earnings per share	$ (2.17)	$ (0.60)	$ (0.74)	$ (1.24)	$ 0.02	$ 0.60	$ 1.00	$ 0.80	$ (4.76)	$ 2.41	$ 3.67