Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	May 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Non-interest expense expenditures related to the acquisition		$ 732,960	$ 693,718	$ 654,740
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