Goodwill and Other Intangible Assets - Components of Other Intangible Assets and Related Amortization (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Purchase Value	$ 242,524	$ 244,955
Accumulated Amortization	109,714	85,182
Carrying Value	132,810	159,773
Aggregate amortization expense	26,797	29,470	32,067
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	198,002	198,002
Accumulated Amortization	85,254	65,357
Carrying Value	112,748	132,645
Aggregate amortization expense	19,897	21,905	23,642
Credit Card and Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	22,400	22,400
Accumulated Amortization	10,366	7,800
Carrying Value	12,034	14,600
Aggregate amortization expense	2,566	2,819	3,072
Value of Insurance Business Acquired [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value		2,431
Accumulated Amortization		2,232
Carrying Value		199
Aggregate amortization expense	34	148	158
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	400	400
Accumulated Amortization	400	300
Carrying Value		100
Aggregate amortization expense	100	200	100
Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	11,722	11,722
Accumulated Amortization	9,334	6,729
Carrying Value	2,388	4,993
Aggregate amortization expense	2,605	2,605	4,124
Merchant Processing Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	10,000	10,000
Accumulated Amortization	4,360	2,764
Carrying Value	5,640	7,236
Aggregate amortization expense	$ 1,595	$ 1,793	$ 971