Deposits - Additional Information About Corporation's Deposits (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Banking and Thrift [Abstract]
Deposits from the Certificate of Deposit Account Registry Service (CDARS)	$ 0	$ 2,615
Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB Bancshares, Inc.)	144	7,440
Deposits from foreign sources (primarily Mexico)	774,351	747,008
Deposits not covered by deposit insurance	$ 12,072,653	$ 11,953,367