Goodwill and Other Intangible Assets (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 654,668	$ 654,668
Amortization expense related to intangible assets	$ 3,325	$ 3,520	$ 3,141
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	5 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	10 years
WNB Bancshares, Inc. [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill				$ 118,019
Core deposit intangible asset				$ 9,300