Fair Value Measurements Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financial assets
Cash and due from banks	$ 444,113		$ 455,482
Cash and due from banks, Fair Value	444,113		455,482
Interest-bearing deposits in other financial institutions	571,924		126,018
Interest-bearing deposits in other financial institutions, Fair value	571,924		126,018
Federal funds sold and securities purchased under agreements to resell	16,030		20,745
Federal funds sold and securities purchased under agreements to resell, Fair value	16,030		20,745
Investment securities held to maturity, carrying amount	404,455		175,210
Investment securities held to maturity, fair value	413,067		169,889
Investment securities available for sale, at fair value	5,396,812		5,250,585
Investment securities available for sale, at fair value	5,396,812		5,250,585
Federal Home Loan Bank and Federal Reserve Bank stocks, carrying amount	189,107		181,249
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	189,107		181,249
Loans held for sale	154,935		64,738
Loans held for sale, fair value	156,423		64,738
Loans, net	17,327,544		15,627,946
Loans, net Fair value	17,427,647		15,599,094
Bank owned life insurance, carrying amount	574,154		568,413
Bank owned life insurance, Fair value	574,154		568,413
Accrued interest receivable, carrying amount	67,573		66,308
Accrued interest receivable, Fair value	67,573		66,308
Interest rate-related agreements, carrying amount	33,023		42,980
Interest rate-related agreements, fair value	33,023		42,980
Foreign currency exchange forwards	2,140		748
Foreign currency exchange forwards, Fair value	2,140		748
Interest rate lock commitments to originate residential mortgage loans held for sale	1,947		416
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	1,947		416
Forward commitments to sell residential mortgage loans, carrying value	0		1,301
Forward commitments to sell residential mortgage loans, fair value	0		1,301
Purchased option	6,054		7,328
Purchased option, at fair value	6,054		7,328
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits	17,192,049		15,581,971
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	17,192,049		15,581,971
Brokered CDs and other time deposits	1,571,455		1,685,196
Brokered CDs and other time deposits, Fair value	1,571,455		1,687,198
Short-term funding	1,068,288		740,926
Short-term funding, Fair value	1,068,288		740,926
Long-term funding	3,930,117		3,087,267
Long-term funding, fair value	3,975,605		3,085,893
Accrued interest payable	9,530		7,994
Accrued interest payable, Fair value	9,530		7,994
Interest rate-related agreements	35,372		45,815
Interest rate-related agreements, Fair value	35,372		45,815
Foreign currency exchange forwards	1,957		655
Foreign currency exchange forwards, Fair value	1,957		655
Standby letters of credit (1), carrying amount	3,542	[1]	3,754	[1]
Standby letters of credit (1), Fair value	3,542	[1]	3,754	[1]
Forward commitments to sell residential mortgage loans	2,435		0
Forward commitments to sell residential mortgage loans, fair value	2,435		0
Written option	6,054		7,328
Written option, at fair value	6,054		7,328
Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and due from banks, Fair Value	444,113		455,482
Interest-bearing deposits in other financial institutions, Fair value	571,924		126,018
Federal funds sold and securities purchased under agreements to resell, Fair value	16,030		20,745
Investment securities held to maturity, fair value	0		0
Investment securities available for sale, at fair value	3,957		4,240
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	0		0
Loans held for sale, fair value	0		0
Loans, net Fair value	0		0
Bank owned life insurance, Fair value	0		0
Accrued interest receivable, Fair value	67,573		66,308
Interest rate-related agreements, fair value	0		0
Foreign currency exchange forwards, Fair value	0		0
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	0		0
Forward commitments to sell residential mortgage loans, fair value	0		0
Purchased option, at fair value	0		0
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	0		0
Brokered CDs and other time deposits, Fair value	0		0
Short-term funding, Fair value	0		0
Long-term funding, fair value	0		0
Accrued interest payable, Fair value	9,530		7,994
Interest rate-related agreements, Fair value	0		0
Foreign currency exchange forwards, Fair value	0		0
Standby letters of credit (1), Fair value	0	[1]	0	[1]
Forward commitments to sell residential mortgage loans, fair value	0		0
Written option, at fair value	0		0
Fair Value, Inputs, Level 2 [Member]
Financial assets
Cash and due from banks, Fair Value	0		0
Interest-bearing deposits in other financial institutions, Fair value	0		0
Federal funds sold and securities purchased under agreements to resell, Fair value	0		0
Investment securities held to maturity, fair value	413,067		169,889
Investment securities available for sale, at fair value	5,392,655		5,246,046
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	189,107		181,249
Loans held for sale, fair value	156,423		64,738
Loans, net Fair value	0		0
Bank owned life insurance, Fair value	574,154		568,413
Accrued interest receivable, Fair value	0		0
Interest rate-related agreements, fair value	33,023		42,980
Foreign currency exchange forwards, Fair value	2,140		748
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	0		0
Forward commitments to sell residential mortgage loans, fair value	0		0
Purchased option, at fair value	6,054		7,328
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	0		0
Brokered CDs and other time deposits, Fair value	1,571,455		1,687,198
Short-term funding, Fair value	1,068,288		740,926
Long-term funding, fair value	3,975,605		3,085,893
Accrued interest payable, Fair value	0		0
Interest rate-related agreements, Fair value	35,372		45,815
Foreign currency exchange forwards, Fair value	1,957		655
Standby letters of credit (1), Fair value	3,542	[1]	3,754	[1]
Forward commitments to sell residential mortgage loans, fair value	0		0
Written option, at fair value	6,054		7,328
Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and due from banks, Fair Value	0		0
Interest-bearing deposits in other financial institutions, Fair value	0		0
Federal funds sold and securities purchased under agreements to resell, Fair value	0		0
Investment securities held to maturity, fair value	0		0
Investment securities available for sale, at fair value	200		299
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	0		0
Loans held for sale, fair value	0		0
Loans, net Fair value	17,427,647		15,599,094
Bank owned life insurance, Fair value	0		0
Accrued interest receivable, Fair value	0		0
Interest rate-related agreements, fair value	0		0
Foreign currency exchange forwards, Fair value	0		0
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	1,947		416
Forward commitments to sell residential mortgage loans, fair value	0		1,301
Purchased option, at fair value	0		0
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	17,192,049		15,581,971
Brokered CDs and other time deposits, Fair value	0		0
Short-term funding, Fair value	0		0
Long-term funding, fair value	0		0
Accrued interest payable, Fair value	0		0
Interest rate-related agreements, Fair value	0		0
Foreign currency exchange forwards, Fair value	0		0
Standby letters of credit (1), Fair value	0	[1]	0	[1]
Forward commitments to sell residential mortgage loans, fair value	2,435		0
Written option, at fair value	$ 0		$ 0

[1] (1) The commitment on standby letters of credit was $353 million and $371 million at December 31, 2014 and 2013, respectively. See Note 15 for additional information on the standby letters of credit and for information on the fair value of lending-related commitments.