Fair Value Measurement (Fair Value, by Balance Sheet Grouping) (Details) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 463,817	$ 697,424	$ 917,822	$ 258,014
Cash and Cash Equivalents, Fair Value Disclosure	463,817	697,424
Available-for-sale	3,967,735	3,545,288
Held-to-maturity	2,674,093	2,903,609
Held-to-maturity Securities, Fair Value	2,659,119	2,875,920
Other Investments and Securities, at Cost	148,172	148,654
Other Investments, Fair Value	148,172	148,654
Loans held for sale, Carrying Amount		13,428
Loans held for sale, Fair Value	5,472	13,428
Net originated and acquired loans, Carrying Amount	15,923,254	15,182,498
Covered Loans and Leases Receivable Fair Value Disclosure	170,690	312,659
Accrued interest receivable, Carrying Amount	67,887	63,657
Accrued Interest Receivable, Fair Value	67,887	63,657
Derivatives, Carrying Amount	58,107	55,197
Derivative Asset, Fair Value, Gross Asset	58,107	55,197
Deposits, Carrying Amount	20,108,003	19,504,665
Deposits, Fair Value	20,116,298	19,510,192
Federal funds purchased and securities sold under agreements to repurchase, Carrying Amount	1,037,075	1,272,591
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	1,037,075	1,272,591
Wholesale borrowings, Carrying Amount	580,648	428,071
Wholesale borrowings, Fair Value	582,120	430,676
Long-term debt, Carrying Amount	505,173	505,192
Long-term Debt, Fair Value	503,675	516,476
Accrued Interest payable, Carrying Amount	10,758	9,820
Accrued interest payable, Fair Value	10,758	9,820
Derivatives, Carrying Amount	52,745	55,439
Derivatives, Fair Value	52,745	55,439
Originated Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Carrying Amount	14,013,370	12,398,116
Net originated and acquired loans, Fair Value	13,795,058	12,235,530
Acquired Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Carrying Amount	1,739,194	2,471,723
Net originated and acquired loans, Fair Value	1,796,314	2,564,842
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		697,424
Available-for-sale	2,821	2,974
Held-to-maturity Securities, Fair Value	0	0
Other Investments, Fair Value	0	0
Loans held for sale, Fair Value	0	0
Covered Loans and Leases Receivable Fair Value Disclosure	0	0
Accrued Interest Receivable, Fair Value	0	0
Derivative Asset, Fair Value, Gross Asset	0	0
Deposits, Fair Value	0	0
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	0	0
Wholesale borrowings, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Accrued interest payable, Fair Value	0	0
Derivatives, Fair Value	0	0
Level 1 | Originated Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	0	0
Level 1 | Acquired Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Available-for-sale	3,623,270	3,203,127
Held-to-maturity Securities, Fair Value		2,875,920
Other Investments, Fair Value		148,654
Loans held for sale, Fair Value	5,472	13,428
Covered Loans and Leases Receivable Fair Value Disclosure	0	0
Accrued Interest Receivable, Fair Value	67,887	63,657
Derivative Asset, Fair Value, Gross Asset	58,107	55,197
Deposits, Fair Value	20,116,298	19,510,192
Federal funds purchased and securities sold under agreements to repurchase, Fair Value		1,272,591
Wholesale borrowings, Fair Value	582,120	430,676
Long-term Debt, Fair Value	503,675	516,476
Accrued interest payable, Fair Value	10,758	9,820
Derivatives, Fair Value	52,745	55,439
Level 2 | Originated Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	0	0
Level 2 | Acquired Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Available-for-sale	341,644	339,187
Held-to-maturity Securities, Fair Value	0	0
Other Investments, Fair Value	0	0
Loans held for sale, Fair Value	0	0
Accrued Interest Receivable, Fair Value	0	0
Derivative Asset, Fair Value, Gross Asset	0	0
Deposits, Fair Value	0	0
Federal funds purchased and securities sold under agreements to repurchase, Fair Value	0	0
Wholesale borrowings, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Accrued interest payable, Fair Value	0	0
Derivatives, Fair Value	0	0
Level 3 | Originated Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	13,795,058	12,235,530
Level 3 | Acquired Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net originated and acquired loans, Fair Value	$ 1,796,314	$ 2,564,842