Fair Value Measurements (Details 5) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financial Assets:
Cash and due from banks	$ 144,290,000	$ 151,969,000
Due from banks - interest-bearing	123,146,000	246,336,000
Loans and leases, net of allowance	14,934,578,000	14,540,407,000
Covered loans, net of allowance	909,563,000	986,223,000	1,438,714,000
FDIC indemnification asset	142,906,000	150,018,000
Investment in FHLB and FRB stock	84,100,000	90,000,000
Financial Liabilities:
Other short-term borrowings	100,000,000
Quoted Prices in Active Markets Level 1
Financial Assets:
Cash and due from banks	144,300,000	152,000,000
Due from banks - interest-bearing	123,100,000	246,300,000
Federal funds sold and securities purchased under repurchase agreements	19,500,000
Federal funds sold		17,100,000
Financial Liabilities:
Federal funds purchased and securities sold under repurchase agreements	703,600,000	1,214,200,000
Other short-term borrowings	100,000,000
Significant Other Observable Inputs Level 2
Financial Assets:
Federal funds sold and securities purchased under repurchase agreements	200,000,000
Securities held-to-maturity	1,434,800,000	1,446,600,000
Loans and leases, net of allowance		4,500,000
Investment in FHLB and FRB stock	84,100,000	90,000,000
Financial Liabilities:
Deposits	22,063,400,000	22,734,500,000
Other short-term borrowings		207,600,000
Long-term debt	713,100,000	698,900,000
Significant Unobservable Inputs Level 3
Financial Assets:
Loans and leases, net of allowance	15,416,900,000	14,984,100,000
Covered loans, net of allowance	975,100,000	1,055,000,000
FDIC indemnification asset	118,800,000	123,900,000
Financial Liabilities:
Deposits	878,300,000	772,400,000
Other short-term borrowings	3,200,000	3,100,000
Long-term debt	72,100,000	75,900,000
Carrying Amount
Financial Assets:
Cash and due from banks	144,300,000	152,000,000
Due from banks - interest-bearing	123,100,000	246,300,000
Federal funds sold and securities purchased under repurchase agreements	219,500,000
Federal funds sold		17,100,000
Securities held-to-maturity	1,400,900,000	1,398,400,000
Loans and leases, net of allowance	14,934,600,000	14,540,400,000
Covered loans, net of allowance	909,600,000	986,200,000
FDIC indemnification asset	142,900,000	150,000,000
Investment in FHLB and FRB stock	84,100,000	90,000,000
Financial Liabilities:
Deposits	22,937,600,000	23,502,400,000
Federal funds purchased and securities sold under repurchase agreements	703,600,000	1,214,200,000
Other short-term borrowings	103,200,000	209,600,000
Long-term debt	703,000,000	706,100,000
Fair Value
Financial Assets:
Cash and due from banks	144,300,000	152,000,000
Due from banks - interest-bearing	123,100,000	246,300,000
Federal funds sold and securities purchased under repurchase agreements	219,500,000
Federal funds sold		17,100,000
Securities held-to-maturity	1,434,800,000	1,446,600,000
Loans and leases, net of allowance	15,416,900,000	14,988,600,000
Covered loans, net of allowance	975,100,000	1,055,000,000
FDIC indemnification asset	118,800,000	123,900,000
Investment in FHLB and FRB stock	84,100,000	90,000,000
Financial Liabilities:
Deposits	22,941,700,000	23,506,900,000
Federal funds purchased and securities sold under repurchase agreements	703,600,000	1,214,200,000
Other short-term borrowings	103,200,000	210,700,000
Long-term debt	$ 785,200,000	$ 774,800,000