Earnings Per Share - Calculations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Calculation of Basic Earnings Per Share:
Net Income	$ 11,863	$ 4,416	$ 8,029	$ 20,367	$ 8,619	$ 5,119	$ 6,294	$ 21,109	$ 44,675	$ 41,140	$ 36,092
Weighted shares outstanding - Basic (in shares)									15,570,539	15,094,423	14,551,308
Basic Earnings Per Share (in usd per share)	$ 0.73	$ 0.29	$ 0.52	$ 1.33	$ 0.56	$ 0.34	$ 0.41	$ 1.45	$ 2.87	$ 2.73	$ 2.48
Calculation of Diluted Earnings Per Share:
Net Income	$ 11,863	$ 4,416	$ 8,029	$ 20,367	$ 8,619	$ 5,119	$ 6,294	$ 21,109	$ 44,675	$ 41,140	$ 36,092
Reconciliation of Denominator:
Weighted shares outstanding - Basic (in shares)									15,570,539	15,094,423	14,551,308
Share-based Compensation									42,552	48,950	53,636
Adjusted denominator — Diluted									15,613,091	15,143,373	14,604,944
Diluted Earnings Per Share (in usd per share)	$ 0.73	$ 0.29	$ 0.52	$ 1.33	$ 0.56	$ 0.33	$ 0.41	$ 1.44	$ 2.86	$ 2.72	$ 2.47