Derivative Instruments (Derivative Instruments Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Derivative Assets [Abstract]
Derivative Fair Value Of Free Standing Derivative Asset		$ 363,772	$ 301,270
Gross Amounts Offset in the Balance Sheet		(26,575)	(30,096)
Net Amounts Presented in the Balance Sheet		337,197	271,174
Derivative Asset, Fair Value of Collateral	[1]	(48,024)	(20,888)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[2]	(305,658)	(245,038)
Net Amount		(16,485)	5,248
Derivative Liabilities [Abstract]
Derivative Fair Value Of Free Standing Derivative Liability		52,023	54,921
Gross Amounts Offset in the Balance Sheet		(26,575)	(30,096)
Net Amounts Presented in the Balance Sheet		25,448	24,825
Gross Amounts Not Offset in the Balance Sheet - Financial Instruments	[3]	(74,680)	(47,149)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[4]	(20,078)	(12,540)
Net Amount		$ (69,310)	$ (34,864)

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