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
	Mar. 31, 2015	Mar. 31, 2014
Numerator for Earnings per Share-Basic:
Net income	$ 12,835	$ 14,033
Less: Income allocated to participating shares	46	35
Net Income Allocated to Shareholders	12,789	13,998
Numerator for Earnings per Share-Diluted:
Net income	12,835	14,033
Net Income Available to Shareholders	$ 12,835	$ 14,033
Denominators:
Weighted Average Shares Outstanding-Basic	31,232,075	29,660,794
Add: Potentially dilutive shares	28,873	37,253
Denominator for Treasury Stock Method-Diluted	31,260,948	29,698,047
Weighted Average Shares Outstanding-Basic	31,232,075	29,660,794
Add: Average participating shares outstanding	111,774	74,237
Denominator for Two-Class Method-Diluted	31,343,849	29,735,031
Earnings per share—basic (in dollars per share)	$ 0.41	$ 0.47
Earnings per share—diluted (in dollars per share)	$ 0.41	$ 0.47
Warrants [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	517,012	517,012
Stock Options [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	155,500	428,863
Restricted Stock [Member]
Denominators:
Anti-dilutive excluded from potentially dilutive shares	82,901	36,984