Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2012

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The cost, net unrealized holding gains, net unrealized holding losses and fair value of available-for-sale investments by types and classes of security at December 31, 2012 consisted of the following:

At December 31, 2012	Cost		Net unrealized holding gains		Net unrealized holding losses			Fair Value
Available-for-sale - included in cash equivalents:
Money market funds and other	$	53,549	$	—	$	—		$	53,549
Available-for-sale - included in short-term marketable securities:
U.S. treasury securities	4,510		—		—			4,510
U.S. government-sponsored enterprise securities	1,065		—		—			1,065
Corporate debt securities	14,933		—		(3		)	14,930
Certificates of deposit	1,800		—		—			1,800
	$	75,857	$	—	$	(3	)	$	75,854

The cost, net unrealized holding gains, net unrealized holding losses and fair value of available-for-sale investments by types and classes of security at December 31, 2011 consisted of the following:

At December 31, 2011	Cost		Net unrealized holding gains		Net unrealized holding losses			Fair Value
Available-for-sale - included in cash equivalents:
Corporate debt securities	$	24,010	$	—	$	—		$	24,010
U.S. government-sponsored enterprise securities	4,000		—		—			4,000
Money market funds and other	40,793		—		—			40,793
Available-for-sale - included in short-term marketable securities:
Municipal notes	9,295		—		—			9,295
U.S. treasury securities	7,501		—		—			7,501
U.S. government-sponsored enterprise securities	16,506		—		(1		)	16,505
Corporate debt securities	12,704		1		—			12,705
	$	114,809	$	1	$	(1	)	$	114,809