Summary of Significant Accounting Policies - Computation of Basic and Diluted Earnings per Share (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
Numerators:
Net income	$ 14,762	$ 15,162	$ 12,074	$ 9,567	$ 7,461	$ 6,075	$ 7,762	$ 11,147	$ 51,565	$ 32,445	$ 48,097
Denominators:
Basic weighted average common shares outstanding (in shares)	33,231,716	33,307,312	33,417,079	33,236,259	32,986,276	32,890,475	32,812,155	32,523,490	33,298,104	32,804,606	32,750,178
Dilutive effect of share based awards (in shares)									880,236	831,987	1,092,760
Diluted weighted average common shares outstanding (in shares)	34,272,731	34,180,635	34,207,973	34,051,971	33,761,462	33,676,665	33,673,669	33,428,544	34,178,340	33,636,593	33,842,938
Earnings Per Share:
Basic (in dollars per share)	$ 0.44	$ 0.46	$ 0.36	$ 0.29	$ 0.23	$ 0.18	$ 0.24	$ 0.34	$ 1.55	$ 0.99	$ 1.47
Diluted (in dollars per share)	$ 0.43	$ 0.44	$ 0.35	$ 0.28	$ 0.22	$ 0.18	$ 0.23	$ 0.33	$ 1.51	$ 0.96	$ 1.42
Weighted average common shares considered anti-dilutive in computing diluted earnings per share (in shares)									73,896	114,395	268,219