Borrowed Funds - Long-term Debt Maturities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term advances from the FHLB	$ 65,944,000	$ 65,989,000
Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Long-term advances from the FHLB	25,946,487,000	25,980,642,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 7/21/2014 Maturity, 2.31% Interest Rate
Debt Instrument [Line Items]
Interest Rate	2.31%	2.31%
Long-term advances from the FHLB	10,000,000,000	10,000,000,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 7/21/2014 Maturity, 2.62% Interest Rate
Debt Instrument [Line Items]
Interest Rate	2.62%	2.62%
Long-term advances from the FHLB	5,000,000,000	5,000,000,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 1/11/2015 Maturity
Debt Instrument [Line Items]
Interest Rate	2.99%	2.99%
Long-term advances from the FHLB	5,000,000,000	5,000,000,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 4/27/2015 Maturity
Debt Instrument [Line Items]
Interest Rate	2.97%	2.97%
Long-term advances from the FHLB	5,000,000,000	5,000,000,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 10/29/2018 Maturity
Debt Instrument [Line Items]
Interest Rate	0.25%	0.25%
Long-term advances from the FHLB	702,678,000	719,690,000
Federal Home Loan Bank Advances | Long-term Advances from the FHLB, 12/19/2023 Maturity
Debt Instrument [Line Items]
Interest Rate	2.00%	2.00%
Long-term advances from the FHLB	$ 243,809,000	$ 260,952,000