Fair Value Measurements (Marketable Debt Securities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Amortized Cost, Total	$ 22,311	$ 21,111
Gross Unrealized Gains, Total	249	220
Gross Unrealized Losses, Total	(1)	(9)
Marketable securities, at fair value	22,559	21,322
Other-than-temporary Impairments, Investments	0	0
Municipal Bonds - Available For Sale [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Amortized Cost, Total	22,311	21,111
Gross Unrealized Gains, Total	249	220
Gross Unrealized Losses, Total	(1)	(9)
Marketable securities, at fair value	22,559	21,322
Other-than-temporary Impairments, Investments	$ 0	$ 0

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

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