Net Income Per Share (Calculation of Net Income per Common 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
Earnings Per Share [Abstract]
Net income	$ 12,802	$ 10,995	$ 10,333	$ 11,225	$ 9,148	$ 11,142	$ 6,982	$ 10,928	$ 45,355	$ 38,200	$ 44,422
Basic:
Basic weighted average EPS shares									24,609,000	25,047,000	24,961,000
Basic net income per share	$ 0.53	$ 0.45	$ 0.42	$ 0.45	$ 0.37	$ 0.44	$ 0.28	$ 0.44	$ 1.84	$ 1.53	$ 1.78
Diluted:
Basic weighted average EPS shares									24,609,000	25,047,000	24,961,000
Dilutive common stock equivalents									89,000	92,000	114,000
Dilutive EPS shares									24,698,000	25,139,000	25,075,000
Diluted net income per share	$ 0.52	$ 0.45	$ 0.42	$ 0.45	$ 0.36	$ 0.44	$ 0.28	$ 0.43	$ 1.84	$ 1.52	$ 1.77
Anti-dilutive shares									7,000	56,000	164,000