Earnings Per Common Share - Summary of Earnings Per Common 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 both basic and diluted earnings per common share:
Net income	$ 18,875	$ 17,017	$ 35,296	$ 33,037
Denominator:
Total average basic common shares outstanding	29,242,180	29,245,201	29,212,347	29,228,355
Effect of dilutive stock options and warrant	79,747	63,605	81,077	59,663
Total diluted average common shares outstanding	29,321,927	29,308,806	29,293,424	29,288,018
Earnings per common share - basic	$ 0.65	$ 0.58	$ 1.21	$ 1.13
Earnings per common share - diluted	$ 0.64	$ 0.58	$ 1.20	$ 1.13