Derivative Instruments Offsetting Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Offsetting Assets [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	$ 122,236	$ 390,809
Gross Amounts Offset In Statement Of Financial Position	(99,620)	(68,689)
Net Amounts Of Assets Presented In Statement Of Financial Position	22,616	322,120
Financial Instruments And Collateral	(22,616)	(203,437)
Net Amount	0	118,683
Offsetting Assets [Member] | Derivative [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	99,620	187,372
Gross Amounts Offset In Statement Of Financial Position	(99,620)	(68,689)
Net Amounts Of Assets Presented In Statement Of Financial Position	0	118,683
Financial Instruments And Collateral	0	0
Net Amount	0	118,683
Offsetting Assets [Member] | Offsetting Securities Purchased Under Agreements To Resell [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	22,616	203,437
Gross Amounts Offset In Statement Of Financial Position	0	0
Net Amounts Of Assets Presented In Statement Of Financial Position	22,616	203,437
Financial Instruments And Collateral	(22,616)	(203,437)
Net Amount	0	0
Offsetting Liabilities [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	151,872	68,689
Gross Amounts Offset In Statement Of Financial Position	(99,851)	(68,689)
Net Amounts Of Assets Presented In Statement Of Financial Position	52,021	0
Financial Instruments And Collateral	(118,177)	0
Net Amount	(66,156)	0
Offsetting Liabilities [Member] | Derivative [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	151,872	68,689
Gross Amounts Offset In Statement Of Financial Position	(99,851)	(68,689)
Net Amounts Of Assets Presented In Statement Of Financial Position	52,021	0
Financial Instruments And Collateral	(118,177)	0
Net Amount	(66,156)	0
Offsetting Liabilities [Member] | Offsetting Securities Sold Under Agreements To Repurchase [Member]
Offsetting Of Financial Assets And Liabillities [Line Items]
Gross Amounts Of Recognized Financial Instruments	0	0
Gross Amounts Offset In Statement Of Financial Position	0	0
Net Amounts Of Assets Presented In Statement Of Financial Position	0	0
Financial Instruments And Collateral	0	0
Net Amount	$ 0	$ 0