Financial Derivatives - Narrative (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Financial derivatives, at fair value	$ 69,995,000	$ 75,708,000
Derivative, Collateral [Abstract]
Collateral Pledged	29,788,000	11,320,000
Additional Collateral, Aggregate Fair Value	51,900,000	63,500,000
Notional Disclosures [Abstract]
Derivative, Notional Amount	6,671,380,000	6,691,851,000
Excluding netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Financial derivatives, at fair value	79,100,000	92,000,000
Credit exposure to interest rate swap counterparties	8,100,000	25,100,000
Netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Financial derivatives, at fair value	81,700,000	74,800,000
Credit exposure to interest rate swap counterparties	1,300,000	3,300,000
Uncollateralized [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	1,300,000	3,000,000
Cash [Member]
Derivative, Collateral [Abstract]
Collateral Received	0	0
Collateral Pledged	29,800,000	9,800,000
Securities Pledged as Collateral [Member]
Derivative, Collateral [Abstract]
Collateral Pledged	0	1,500,000
Exchange Cleared [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	3,800,000,000	2,300,000,000
Interest Rate Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 6,600,000,000	$ 6,600,000,000