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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 8,267	$ 15,089	$ 14,741	$ 15,112	$ 13,316	$ 13,474	$ 10,647	$ 10,813	$ 53,209	$ 48,250	$ 45,355
Basic:
Basic weighted average EPS shares									24,175,000	24,120,000	24,609,000
Basic net income per share	$ 0.34	$ 0.62	$ 0.61	$ 0.63	$ 0.55	$ 0.56	$ 0.45	$ 0.45	$ 2.2	$ 2	$ 1.84
Diluted:
Basic weighted average EPS shares									24,175,000	24,120,000	24,609,000
Dilutive common stock equivalents									32,000	29,000	89,000
Dilutive EPS shares									24,207,000	24,149,000	24,698,000
Diluted net income per share	$ 0.34	$ 0.62	$ 0.61	$ 0.63	$ 0.55	$ 0.56	$ 0.44	$ 0.45	$ 2.2	$ 2	$ 1.84
Anti-dilutive shares									3,000	3,000	7,000