Net Income Per Share (Calculation of Net Income per Common Share (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Calculation Of Net Income Per Common Share [Abstract]
Net income	$ 9,148,000	$ 11,142,000	$ 6,982,000	$ 10,928,000	$ 9,613,000	$ 12,089,000	$ 12,162,000	$ 10,558,000	$ 38,200,000	$ 44,422,000	$ 36,554,000
Basic:
Basic weighted average EPS shares									25,047,000	24,961,000	24,573,000
Basic net income per share	$ 0.37	$ 0.44	$ 0.28	$ 0.44	$ 0.38	$ 0.48	$ 0.49	$ 0.42	$ 1.53	$ 1.78	$ 1.49
Diluted:
Basic weighted average EPS shares									25,047,000	24,961,000	24,573,000
Dilutive common stock equivalents									92,000	114,000	84,000
Dilutive EPS shares									25,139,000	25,075,000	24,657,000
Diluted net income per share	$ 0.36	$ 0.44	$ 0.28	$ 0.43	$ 0.38	$ 0.48	$ 0.49	$ 0.42	$ 1.52	$ 1.77	$ 1.48
Anti-dilutive shares									56,000	164,000	421,000