Derivative Instruments Offsetting Balance Sheet (Details) (Derivative [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Offsetting Assets [Member]
Offsetting of Financial Assets and Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments	$ 153,312		$ 118,846
Gross Amounts Offset in Statement of Financial Position	(14,108)		(24,288)
Net Amounts of Assets Presented in Statement of Financial Position	139,204		94,558
Financial Instruments And Collateral	(134,839)	[1]	(82,602)	[1]
Net Amount	4,365		11,956
Offsetting Liabilities [Member]
Offsetting of Financial Assets and Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments	16,185		21,249
Gross Amounts Offset in Statement of Financial Position	(16,185)		(21,249)
Net Amounts of Assets Presented in Statement of Financial Position	0		0
Financial Instruments And Collateral	0	[1]	0	[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.