Derivative Instruments (Derivative Instruments Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Derivative Assets [Abstract]
Derivative Fair Value Of Free Standing Derivative Asset		$ 222,427	$ 283,094
Gross Amounts Offset in the Balance Sheet		(23,074)	(27,028)
Net Amounts Presented in the Balance Sheet		199,353	256,066
Derivative Asset, Fair Value of Collateral	[1]	(18,439)	(16,913)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[2]	(194,125)	(254,498)
Net Amount		(13,211)	(15,345)
Derivative Liabilities [Abstract]
Derivative Fair Value Of Free Standing Derivative Liability		34,395	48,571
Gross Amounts Offset in the Balance Sheet		(23,074)	(27,028)
Net Amounts Presented in the Balance Sheet		11,321	21,543
Gross Amounts Not Offset in the Balance Sheet - Financial Instruments	[3]	(76,173)	(95,863)
Gross Amounts Not Offset in the Balance Sheet - Cash Collateral Pledged/Received	[4]	(1,111)	(1,441)
Net Amount		$ (65,963)	$ (75,761)

[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.