Goodwill and Other Intangible Assets - Components of Other Intangible Assets and Related Amortization (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Purchase Value	$ 234,777	$ 242,524
Accumulated Amortization	127,239	109,714
Carrying Value	107,538	132,810
Aggregate amortization expense	24,184	26,797	$ 29,470
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	190,655	198,002
Accumulated Amortization	97,026	85,254
Carrying Value	93,629	112,748
Aggregate amortization expense	18,031	19,897	21,905
Credit Card and Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	22,400	22,400
Accumulated Amortization	12,735	10,366
Carrying Value	9,665	12,034
Aggregate amortization expense	2,369	2,566	2,819
Value of Insurance Business Acquired [Member]
Finite-Lived Intangible Assets [Line Items]
Aggregate amortization expense		34	148
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value		400
Accumulated Amortization		400
Aggregate amortization expense		100	200
Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	11,722	11,722
Accumulated Amortization	11,722	9,334
Carrying Value		2,388
Aggregate amortization expense	2,388	2,605	2,605
Merchant Processing Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	10,000	10,000
Accumulated Amortization	5,756	4,360
Carrying Value	4,244	5,640
Aggregate amortization expense	$ 1,396	$ 1,595	$ 1,793