Margin Account Loan (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Margin Account Loan [Abstract]
Line of credit facility initiation date	Jul. 26, 2011
Interest rate during period (percent)	2.50%
Reduction in Wells Fargo base rate (percent)	2.75%
Margin account loan liability	$ 7,051	$ 7,051
Marketable securities – restricted	14,837	14,500
Increase in accrued interest	$ 45

Investments in debt and equity securities which are categorized neither as trading securities nor held-to-maturity securities, which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer, and that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.

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

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Reference 7: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 8: http://www.xbrl.org/2003/role/presentationRef

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-Name Federal Regulation (FR)

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-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

+ Details