Investments (Tables)

9 Months Ended

Sep. 30, 2012

Investments [Abstract]

Unrealized gains and losses related to our investments designated as available-for-sale

	September 30, 2012
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	2,804	$	—	$	—		$	2,804
Auction rate municipal securities		882		41		—			923
Total investments	$	3,686	$	41	$	—		$	3,727
	December 31, 2011
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate obligations	$	11,260	$	—	$	(1	)	$	11,259
U.S. Government notes		14,049		7		(4	)		14,052
Auction rate municipal securities		893		9		—			902
Total investments	$	26,202	$	16	$	(5	)	$	26,213

Schedule of net carrying value (amortized cost) and estimated fair value of investments

	Amortized Cost		Estimated Fair Value
Due in one year or less	$	2,804	$	2,804
Due after one year through three years		—		—
Due after three years		882		923
Total investments	$	3,686	$	3,727

Schedule of unrealized losses and fair values of investments in unrealized loss position aggregated by investment category and length of time that individual securities have been in a continuous loss position

	September 30, 2012				December 31, 2011
	Less than 12 Months				Less than 12 Months
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate obligations	$	—	$	—	$	3,810	$	(1	)
U.S. Government notes		—		—		6,758		(4	)
	$	—	$	—	$	10,568	$	(5	)