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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator for Earnings per Share-Basic:
Net income	$ 14,720	$ 14,103	$ 28,753	$ 26,433
Less: Income allocated to participating shares	29	36	64	81
Net Income Allocated to Shareholders	14,691	14,067	28,689	26,352
Numerator for Earnings per Share-Diluted:
Net income	14,720	14,103	28,753	26,433
Net Income Available to Shareholders	$ 14,720	$ 14,103	$ 28,753	$ 26,433
Denominators:
Weighted Average Shares Outstanding-Basic	29,684,300	29,654,018	29,672,611	29,637,825
Add: Dilutive potential shares	16,894	23,858	27,559	41,319
Denominator for Treasury Stock Method-Diluted	29,701,194	29,677,876	29,700,170	29,679,144
Weighted Average Shares Outstanding-Basic	29,684,300	29,654,018	29,672,611	29,637,825
Add: Average participating shares outstanding	58,973	74,994	66,563	91,530
Denominator for Two-Class Method-Diluted	29,743,273	29,729,012	29,739,174	29,729,355
Earnings per share—basic (in dollars per share)	$ 0.49	$ 0.47	$ 0.97	$ 0.89
Earnings per share—diluted (in dollars per share)	$ 0.49	$ 0.47	$ 0.97	$ 0.89
Warrants [Member]
Denominators:
Anti-dilutive excluded from dilutive potential shares	517,012	517,012	517,012	517,012
Stock Options [Member]
Denominators:
Anti-dilutive excluded from dilutive potential shares	428,493	629,570	428,676	642,499
Restricted Stock [Member]
Denominators:
Anti-dilutive excluded from dilutive potential shares	42,079	51,136	39,005	50,211