Financial Derivatives - Narrative (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Financial derivatives Liability, at fair value	$ 73,887,000	$ 75,708,000
Collateral Pledged	14,223,000	11,320,000
Additional Collateral, Aggregate Fair Value	54,400,000	63,500,000
Derivative, Notional Amount	6,628,072,000	6,691,851,000
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	150,000,000	0
Excluding netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	19,300,000	25,100,000
Financial derivatives Liability, at fair value	81,500,000	(92,000,000)
Netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	2,300,000	3,300,000
Uncollateralized [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	2,300,000	3,000,000
Cash [Member]
Derivative [Line Items]
Collateral Received	0	0
Collateral Pledged	14,200,000	9,800,000
Securities Pledged as Collateral [Member]
Derivative [Line Items]
Collateral Pledged	0	1,500,000
Counterparty level [Member] | Netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Financial derivatives Liability, at fair value	68,600,000	74,800,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	6,600,000,000
Not Designated as Hedging Instrument [Member] | Derivative Contract Type - Centrally Cleared [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 3,100,000,000