Fair Value Measurements (Details 5) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Financial Assets:
Cash and due from banks	$ 425,427,000	$ 183,227,000
Due from banks - interest bearing	434,297,000	552,719,000
Federal funds sold and securities purchased under resale agreements	205,000,000	200,000,000
Securities purchased under resale agreements	200,000,000	200,000,000
Securities held-to-maturity	3,165,068,000	2,883,935,000
Loans and leases, net of allowance	17,445,595,000	16,867,854,000
Covered loans, net of allowance	654,855,000	700,989,000
FDIC indemnification asset	84,851,000	89,227,000
Investment in FHLB and FRB stock	57,200,000	64,400,000
Quoted Prices in Active Markets Level 1
Financial Assets:
Cash and due from banks	425,400,000	183,200,000
Due from banks - interest bearing	434,300,000	552,700,000
Federal funds sold and securities purchased under resale agreements	5,000,000
Significant Other Observable Inputs Level 2
Financial Assets:
Federal funds sold and securities purchased under resale agreements	201,500,000
Securities purchased under resale agreements		200,500,000
Securities held-to-maturity	3,165,100,000	2,883,900,000
Investment in FHLB and FRB stock	57,200,000	64,400,000
Financial Liabilities:
Deposits	25,103,900,000	24,990,800,000
Long-term debt	713,000,000	697,800,000
Significant Unobservable Inputs Level 3
Financial Assets:
Loans and leases, net of allowance	18,005,100,000	17,362,900,000
Covered loans, net of allowance	698,800,000	739,500,000
FDIC indemnification asset	70,100,000	74,300,000
Financial Liabilities:
Deposits	630,300,000	691,400,000
Other short-term borrowings	4,100,000	3,900,000
Long-term debt	88,700,000	91,100,000
Carrying Amount
Financial Assets:
Cash and due from banks	425,400,000	183,200,000
Due from banks - interest bearing	434,300,000	552,700,000
Federal funds sold and securities purchased under resale agreements	205,000,000
Securities purchased under resale agreements		200,000,000
Securities held-to-maturity	3,203,000,000	2,957,800,000
Loans and leases, net of allowance	17,445,600,000	16,867,900,000
Covered loans, net of allowance	654,900,000	701,000,000
FDIC indemnification asset	84,900,000	89,200,000
Investment in FHLB and FRB stock	57,200,000	64,400,000
Financial Liabilities:
Deposits	25,731,800,000	25,679,400,000
Other short-term borrowings	4,100,000	3,900,000
Long-term debt	733,500,000	736,000,000
Fair Value
Financial Assets:
Cash and due from banks	425,400,000	183,200,000
Due from banks - interest bearing	434,300,000	552,700,000
Federal funds sold and securities purchased under resale agreements	206,500,000
Securities purchased under resale agreements		200,500,000
Securities held-to-maturity	3,165,100,000	2,883,900,000
Loans and leases, net of allowance	18,005,100,000	17,362,900,000
Covered loans, net of allowance	698,800,000	739,500,000
FDIC indemnification asset	70,100,000	74,300,000
Investment in FHLB and FRB stock	57,200,000	64,400,000
Financial Liabilities:
Deposits	25,734,200,000	25,682,200,000
Other short-term borrowings	4,100,000	3,900,000
Long-term debt	$ 801,700,000	$ 788,900,000