Deposits - Additional Information About Corporation's Deposits (Detail) - USD ($) $ in Thousands	Jun. 30, 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.)	0	7,440
Deposits from foreign sources (primarily Mexico)	760,918	747,008
Deposits not covered by deposit insurance	$ 11,672,042	$ 11,953,367