Financial Derivatives (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified															12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Jul. 02, 2012 Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2012 Fair Value Hedging [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Non-Callable [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Non-Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Basis Swap [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member] Basis Swap [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member] Credit Default Swap [Member]
Derivatives, Fair Value [Line Items]
Notional Amount of Interest Rate Fair Value Hedge Derivatives			$ 950,000	$ 950,000
Fair Value Hedge Assets			0
Fair Value Hedge Liabilities			58,758
Derivative, Weighted-Average Pay Rate					2.20%			4.83%	3.65%	0.33%	0.41%	0.15%	0.43%	0.80%			1.00%
Derivative, Weighted-Average Receive Rate					0.31%			0.32%	0.46%	0.85%	0.96%	0.55%	0.36%	0.38%			0.00%
Derivative, Notional Amount	6,815,268	6,586,530						805,622	1,906,123	4,135,149	4,212,713	245,000	609,262	457,694	59,035	11,200	10,000
Financial derivatives, at fair value	31,173	40,250						357	0	30,338	41,006	6	499	0	0	0	17
Financial derivatives, at fair value	150,682	160,024						91,205	157,520	211	1,302	238	784	2,137	(58)	(12)	0
Derivative, Weighted-Average Forward Price															$ 101.22	$ 129.77
Derivative Credit Risk Valuation Adjustment, Derivative Assets						27	773
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities						$ 584	$ 935