Derivative Instruments (Derivative Instruments Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Derivative Assets [Abstract]
Derivative Fair Value Of Free Standing Derivative Asset		$ 327,453	$ 301,270
Gross Amounts Offset in the Balance Sheet		(28,693)	(30,096)
Net Amounts Presented in the Balance Sheet		298,760	271,174
Derivative Asset, Fair Value of Collateral	[1]	(32,953)	(20,888)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[2]	(265,257)	(245,038)
Net Amount		550	5,248
Derivative Liabilities [Abstract]
Derivative Fair Value Of Free Standing Derivative Liability		45,316	54,921
Gross Amounts Offset in the Balance Sheet		(28,693)	(30,096)
Net Amounts Presented in the Balance Sheet		16,623	24,825
Gross Amounts Not Offset in the Balance Sheet - Financial Instruments	[3]	(74,663)	(47,149)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[4]	(9,409)	(12,540)
Net Amount		$ (67,449)	$ (34,864)

[1] Consists of U.S. Treasury and government securities securities.

[2] Included in cash and cash equivalents, with obligation to return cash collateral recorded in other liabilities.

[3] Included in available-for-sale securities, primarily consists of U.S. Treasury and government agency securities.

[4] Consists of receivable from counterparty, included in other assets.