Fair Value Measurement (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Fair value of Level 3 assets measured on a recurring basis
Other-than-temporary impairments		$ (4)		$ (4)
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Other asset-backed securities [Member]
Fair value of Level 3 assets measured on a recurring basis
Beginning balance	25,397	26,340	24,232	23,710
Principal paydowns	(70)	(94)	(134)	(504)
Other-than-temporary impairments		(4)		(4)
Unrealized gains-instruments still held at the reporting date	1,657	5,436	3,707	9,529
Unrealized losses-instruments still held at the reporting date	(287)	(2,004)	(1,108)	(3,057)
Ending balance	$ 26,697	$ 29,674	$ 26,697	$ 29,674

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

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