Offsetting Assets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Securities Borrowed [Member]
Offsetting Assets [Line Items]
Financial Instruments	$ 0	$ 0
Cash Collateral Pledged	151,768	106,350
Net Amount	0	0
Securities Borrowed Gross [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	151,768	106,350
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	151,768	106,350
Securities Borrowed Net [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	151,768	106,350
Net Amounts of Assets Presented in the Statement of Financial Position	151,768	106,350
Securities Loaned [Member]
Offsetting Assets [Line Items]
Financial Instruments	0	0
Net Amount	0	0
Cash Collateral Received	58,183	12,517
Securities Loaned Gross [Member]
Offsetting Assets [Line Items]
Gross Amounts Offset in the Statement of Financial Position	0	0
Gross Amounts of Recognized Liabilities	58,183	12,517
Net Amounts of Liabilities Presented in the Statement of Financial Position	58,183	12,517
Securities Loaned Net [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Liabilities	58,183	12,517
Net Amounts of Liabilities Presented in the Statement of Financial Position	$ 58,183	$ 12,517