Investments (Tables)

12 Months Ended

Dec. 31, 2012

Unrealized Gains and Losses on Available-for-Sale

The following table summarizes unrealized gains and losses related to our investments designated as available-for-sale (dollars in thousands):

	As of December 31, 2012
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Certificates of deposit	$	2,804	$	—	$	—	$	2,804
Total investments	$	2,804	$	—	$	—	$	2,804

	As of 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

Gross Unrealized Losses and Fair Values of Investments

The following table presents gross unrealized losses and fair values for those investments that were in an unrealized loss position aggregated by investment category and the length of time that individual securities have been in a continuous loss position (dollars in thousands):

	As of December 31, 2012				As of 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	)

Net Carrying Value and Estimated Fair Value of Debt and Equity Securities Available for Sale

The net carrying value and estimated fair value of debt and equity securities available for sale at December 31, 2012, by contractual maturity, are shown below (dollars in thousands). Expected maturities may differ from contractual maturities because the issuers of the securities may have the right or obligation to prepay obligations without prepayment penalties.

	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		—		—
Total investment securities	$	2,804	$	2,804