Financial Derivatives - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Securities Purchased under Agreements to Resell	$ 0	$ 0
Financial derivatives, at fair value	77,199	84,844
Derivative, Collateral [Abstract]
Collateral Pledged	37,986	46,627
Additional Collateral, Aggregate Fair Value	45,200	46,800
Notional Disclosures [Abstract]
Derivative, Notional Amount	8,429,964	6,837,571
Excluding netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	6,400	6,100
Financial derivatives, at fair value	90,100	99,400
Netting [Member] | Including accrued interest [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	0	400
Financial derivatives, at fair value	83,200	93,400
Uncollateralized [Member]
Derivative [Line Items]
Credit exposure to interest rate swap counterparties	0	400
Cash [Member]
Derivative, Collateral [Abstract]
Collateral Received	0	0
Collateral Pledged	38,000	46,600
Securities Pledged as Collateral [Member]
Derivative, Collateral [Abstract]
Collateral Pledged	0	0
Exchange Cleared [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	6,200,000	4,000,000
Interest Rate Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 8,400,000	$ 6,800,000