Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income (loss)		$ 10,089	$ (5,165)	$ 22,371	$ 1,960
Weighted average shares outstanding - basic		17,335,914	17,244,075	17,326,019	17,234,063
Net income (loss) per share	[1]	$ 0.58	$ (0.30)	$ 1.29	$ 0.11
Weighted average shares outstanding - diluted	[2]	17,690,879	17,244,075	17,670,636	17,484,980
Net income (loss) per share	[1]	$ 0.57	$ (0.30)	$ 1.27	$ 0.11

[1] For the quarter ended June 30, 2016, "diluted" loss per share is the same as "basic" loss per share since there was a net loss for the period.

[2] For the quarter ended June 30, 2016, "weighted average shares outstanding - basic" was used to calculate "diluted earnings per share" due to a net loss for the period.