Earnings Per Common Share Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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—basic and diluted
Net income (loss)	$ 10,349	$ 10,309	$ 21,709	$ 23,686	$ 921	$ 22,522	$ 17,247	$ 18,117	$ 66,053	$ 58,807	$ (10,594)
Denominator
Weighted average number of common shares outstanding — basic	41,078	41,094	40,792	40,384	39,991	39,789	39,681	39,438	40,846	39,726	39,188
Effect of dilutive stock options									388	375
Effect of dilutive restricted shares									495	628
Weighted average number of common shares outstanding — diluted	41,879	41,982	41,696	41,324	41,090	40,819	40,750	40,457	41,729	40,729	39,188
Earnings (loss) per common share — basic	$ 0.25	$ 0.25	$ 0.53	$ 0.59	$ 0.02	$ 0.57	$ 0.43	$ 0.46	$ 1.62	$ 1.48	$ (0.27)
Earnings (loss) per common share — diluted	$ 0.25	$ 0.25	$ 0.52	$ 0.57	$ 0.02	$ 0.55	$ 0.42	$ 0.45	$ 1.58	$ 1.44	$ (0.27)
Stock Options And Restricted Shares
Denominator
Anti-dilutive securities excluded from computation of earnings per share									1,734	2,967	4,363