Earnings Per Share - Reconciles Numerators and Denominators of Basic Earnings Per Share with Diluted Earnings 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
Numerator for Earnings per Share-Basic:
Net income	$ 14,660	$ 12,247	$ 43,414	$ 38,680
Less: Income allocated to participating shares	51	33	115	114
Net Income Allocated to Shareholders	14,609	12,214	43,299	38,566
Numerator for Earnings per Share-Diluted:
Net income	14,660	12,247	43,414	38,680
Net Income Available to Shareholders	$ 14,660	$ 12,247	$ 43,414	$ 38,680
Denominators:
Weighted Average Shares Outstanding-Basic	29,693,417	29,658,065	29,679,623	29,644,646
Add: Potentially dilutive shares	21,195	27,535	25,732	35,132
Denominator for Treasury Stock Method-Diluted	29,714,612	29,685,600	29,705,355	29,679,778
Weighted Average Shares Outstanding-Basic	29,693,417	29,658,065	29,679,623	29,644,646
Add: Average participating shares outstanding	102,980	80,240	78,835	87,725
Denominator for Two-Class Method-Diluted	29,796,397	29,738,305	29,758,458	29,732,371
Earnings per share—basic (in dollars per share)	$ 0.49	$ 0.41	$ 1.46	$ 1.30
Earnings per share—diluted (in dollars per share)	$ 0.49	$ 0.41	$ 1.46	$ 1.30
Warrants [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	517,012	517,012	517,012	517,012
Stock Options [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	427,362	612,768	428,233	632,481
Restricted Stock [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	81,785	52,705	53,103	52,593