Earnings Per Share - Reconciliation of Numerator and Denominator of Basic Earnings Per Share with that of 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
Earnings Per Share [Abstract]
Distributed earnings allocated to common stock	$ 22,124	$ 15,586	$ 44,160	$ 31,163
Undistributed earnings allocated to common stock	11,065	6,598	19,093	12,567
Net earnings allocated to common shareholders	$ 33,189	$ 22,184	$ 63,253	$ 43,730
Average common shares outstanding	68,956,123	50,345,733	65,713,854	50,322,783
Equivalents from stock options	197,909	56,461	235,601	59,387
Average diluted shares outstanding	69,154,032	50,402,194	65,949,455	50,382,170
Earnings per basic common share	$ 0.48	$ 0.44	$ 0.96	$ 0.87
Earnings per diluted common share	$ 0.48	$ 0.44	$ 0.96	$ 0.87