Goodwill and Other Intangible Assets - Rollforward of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 832,213	$ 764,248
Goodwill (deductions) additions	873	67,965
Goodwill, Ending Balance	833,086	832,213
Community Banking [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	813,434	745,469
Goodwill (deductions) additions	(1,035)	67,965
Goodwill, Ending Balance	812,399	813,434
Wealth Management [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	8,020	8,020
Goodwill, Ending Balance	8,020	8,020
Insurance [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	8,950	8,950
Goodwill (deductions) additions	1,908
Goodwill, Ending Balance	10,858	8,950
Consumer Finance [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	1,809	1,809
Goodwill, Ending Balance	$ 1,809	$ 1,809