Financial Derivatives - Narrative (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Financial derivatives Liability, at fair value	$ 78,296,000	$ 75,708,000
Collateral Pledged	23,822,000	11,320,000
Additional Collateral, Aggregate Fair Value	61,700,000	63,500,000
Derivative, Notional Amount	6,495,920,000	6,691,851,000
Excluding netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	11,800,000	25,100,000
Financial derivatives Liability, at fair value	91,100,000	(92,000,000)
Netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	1,800,000	3,300,000
Financial derivatives Liability, at fair value	85,500,000	74,800,000
Uncollateralized [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	1,800,000	3,000,000
Cash [Member]
Derivative [Line Items]
Collateral Received	0	0
Collateral Pledged	23,800,000	9,800,000
Securities Pledged as Collateral [Member]
Derivative [Line Items]
Collateral Pledged	0	1,500,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	6,500,000,000	6,600,000,000
Exchange Cleared [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 3,400,000,000	$ 2,300,000,000