Computation of Basic and Diluted (Loss) Earnings per Share under Two-Class Method (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator for basic and diluted (loss) earnings per share:
Net (loss) income	$ (17,004)	$ 23,017	$ (45,606)	$ 41,444
Effect of reallocating undistributed earnings of participating securities		(154)		(290)
Net (loss) income available under the two-class method	$ (17,004)	$ 22,863	$ (45,606)	$ 41,154
Denominator:
Denominator for basic (loss) earnings per share-weighted-average shares	22,999,157	22,947,957	22,987,086	22,948,032
Effect of dilutive potential common shares	0	0	0	0
Denominator for diluted (loss) earnings per share-adjusted weighted-average shares	22,999,157	22,947,957	22,987,086	22,948,032
Basic (loss) earnings per share	$ (0.74)	$ 1.00	$ (1.98)	$ 1.79
Diluted (loss) earnings per share	$ (0.74)	$ 1.00	$ (1.98)	$ 1.79