Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	May. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Non-interest expense expenditures related to the acquisition		$ 693,718	$ 654,740	$ 611,910
WNB Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Purchase price allocation	$ 198,798
Total value of stock issued for consideration	$ 149,700
Common stock number of shares issued for consideration	2,000,000
Amount of cash consideration	$ 49,100
Amortization period of intangible assets acquired		10 years
Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Non-interest expense expenditures related to the acquisition			$ 7,100	$ 1,400