Derivative Instruments (Credit Exposure of Derivative Contracts) (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Credit Exposure of Derivative Contracts [Abstract]
Derivative Assets (Liabilities), at Fair Value, Net		$ 248,968	$ 175,209
Derivative, Collateral, Right to Reclaim Cash	[1]	12,540	0
Derivative Liability, Fair Value of Collateral	[2]	47,149	47,222
Derivative, Collateral, Obligation to Return Cash	[3]	(245,038)	(178,141)
Derivative Asset, Fair Value of Collateral	[4]	(20,888)	(20,260)
Deposits with Clearing Organizations and Others, Securities		(34,898)	(16,333)
Net Credit Exposure On Derivative Contracts		7,833	7,697
Margin Deposit Assets	[5]	$ 11,004	$ 7,976

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

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

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

[4] Consists of U.S. Treasury

[5] Included in other assets.