3. Income Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 7,685	$ 7,673	$ 21,768	$ 20,813
Weighted average basic shares outstanding	1,949	2,007	1,964	2,014
Add: Effect of dilutive securities	17	9	16	5
Weighted average diluted shares outstanding	1,966	2,016	1,980	2,019
Earnings per share:
Basic	$ 3.94	$ 3.82	$ 11.08	$ 10.33
Diluted	$ 3.91	$ 3.81	$ 10.99	$ 10.31