Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash on hand or on deposit required	$ 188,900	$ 175,600
Cash collateral on deposit	16,900	12,100
Foreclosed Assets	$ 2,300	5,300
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	80.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	125.00%
WNB Bancshares, Inc. [Member] | Goodwill [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, Purchase Accounting Adjustments		718
WNB Bancshares, Inc. [Member] | Property, Plant and Equipment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, Purchase Accounting Adjustments		$ (718)