Earnings Per Share - Reconciles Numerators and Denominators of Basic Earnings Per Share and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator for Earnings per Common Share-Basic:
Net Income									$ 67,081	$ 57,910	$ 50,539
Less: Income allocated to participating shares									280	165	147
Net Income Available to Common Shareholders	$ 17,423	$ 18,635	$ 18,188	$ 12,835	$ 14,497	$ 14,660	$ 14,720	$ 14,033	66,801	57,745	50,392
Numerator for Earnings per Common Share-Diluted:
Net Income									$ 67,081	$ 57,910	$ 50,539
Denominators:
Weighted Average Common Shares Outstanding-Basic (in shares)									33,812,990	29,683,103	29,647,231
Add: Dilutive potential common shares (in shares)									35,092	25,621	35,322
Denominator for Treasury Stock Method-Diluted (in shares)									33,848,082	29,708,724	29,682,553
Weighted Average Common Shares Outstanding-Basic (in shares)									33,812,990	29,683,103	29,647,231
Add: Average participating shares outstanding (in shares)									141,558	84,918	86,490
Denominator for Two-Class Method-Diluted									33,954,548	29,768,021	29,733,721
Earnings per common share—basic (in USD per share)									$ 1.98	$ 1.95	$ 1.70
Earnings per common share—diluted (in USD per share)	$ 0.50	$ 0.54	$ 0.52	$ 0.41	$ 0.49	$ 0.49	$ 0.49	$ 0.47	1.98	$ 1.95	$ 1.70
Exercise price of warrants (dollars per share)	$ 31.53								$ 31.53
Warrants
Denominators:
Anti-dilutive excluded from dilutive potential common shares (in shares)									517,012	517,012	517,012
Stock Options
Denominators:
Anti-dilutive excluded from dilutive potential common shares (in shares)									0	419,538	619,418
Restricted Stock
Denominators:
Anti-dilutive excluded from dilutive potential common shares (in shares)									106,466	59,297	51,169