Derivative Instruments Offsetting Balance Sheet (Details) (Derivative [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Offsetting Assets [Member]
Offsetting of Financial Assets and Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments	$ 118,846		$ 73,535
Gross Amounts Offset in Statement of Financial Position	(24,288)		(73,535)
Net Amounts of Assets Presented in Statement of Financial Position	94,558		0
Financial Instruments And Collateral	(82,602)	[1]	0	[1]
Net Amount	11,956		0
Offsetting Liabilities [Member]
Offsetting of Financial Assets and Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments	21,249		94,580
Gross Amounts Offset in Statement of Financial Position	(21,249)		(72,822)
Net Amounts of Assets Presented in Statement of Financial Position	0		21,758
Financial Instruments And Collateral	0	[1]	(21,758)	[1]
Net Amount	$ 0		$ 0

[1] Amounts exclude the excess of collateral received/pledged from/to the counterparty. Prior period has been revised to conform to current period presentation.