Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2011

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The cost, gross unrealized holding gains, gross 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
Money market funds and other	40,793		—		—			40,793
U.S. government-sponsored enterprise securities	4,000		—		—			4,000
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

The cost, gross unrealized holding gains, gross unrealized holding losses and fair value of available-for-sale investments by types and classes of security at December 31, 2010 consisted of the following:

At December 31, 2010	Cost		Net unrealized holding gains		Net unrealized holding losses			Fair Value
Available-for-sale - included in cash equivalents:
U.S. treasury securities	$	5,500	$	—	$	—		$	5,500
Certificates of deposit	325		—		—			325
Money market funds and other	114,217		—		—			114,217
Available-for-sale - included in short-term marketable securities:
U.S. treasury securities	3,115		—		(2		)	3,113
U.S. government-sponsored enterprise securities	26,366		4		—			26,370
Certificates of deposit	1,709		—		—			1,709
	$	151,232	$	4	$	(2	)	$	151,234