Earnings Per Share - Reconciles Numerators and Denominators of Basic Earnings Per Share with Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator for Earnings per Share-Basic:
Net income	$ 18,635	$ 14,660	$ 49,658	$ 43,414
Less: Income allocated to participating shares	81	51	204	115
Net Income Allocated to Shareholders	18,554	14,609	49,454	43,299
Numerator for Earnings per Share-Diluted:
Net income	18,635	14,660	49,658	43,414
Net Income Available to Shareholders	$ 18,635	$ 14,660	$ 49,658	$ 43,414
Denominators:
Weighted Average Shares Outstanding-Basic	34,660,007	29,693,417	33,527,549	29,679,623
Add: Potentially dilutive shares	32,985	21,195	33,980	25,732
Denominator for Treasury Stock Method-Diluted	34,692,992	29,714,612	33,561,529	29,705,355
Weighted Average Shares Outstanding-Basic	34,660,007	29,693,417	33,527,549	29,679,623
Add: Average participating shares outstanding	151,972	102,980	138,441	78,835
Denominator for Two-Class Method-Diluted	34,811,979	29,796,397	33,665,990	29,758,458
Earnings per share—basic (in dollars per share)	$ 0.54	$ 0.49	$ 1.48	$ 1.46
Earnings per share—diluted (in dollars per share)	0.54	$ 0.49	1.48	$ 1.46
Anti-dilutive warrants - exercise price (in USD per share)	$ 31.53		$ 31.53
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	155,500	427,362	155,500	428,233
Restricted Stock [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	118,987	81,785	104,461	53,103