Investments (Tables)

6 Months Ended

Jun. 30, 2012

Investments

Summary of short- and long-term investments

	June 30, 2012
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term investments:
Corporate debt securities
Due in one year or less	$	57,598	$	86	$	(37	)	$	57,647
Due in one to three years	52,577		64		(70		)	52,571
U.S. treasury and government agency securities
Due in one year or less	17,972		95		—			18,067
Due in one to three years	40,709		104		(4		)	40,809
Commercial paper
Due in one year or less	7,487		—		(10		)	7,477
Total investments	$	176,343	$	349	$	(121	)	$	176,571

	December 31, 2011
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term investments:
Corporate debt securities
Due in one year or less	$	74,687	$	81	$	(115	)	$	74,653
Due in one to three years	19,950		73		(50		)	19,973
U.S. treasury and government agency securities
Due in one year or less	26,770		67		(7		)	26,830
Due in one to three years	21,028		228		—			21,256
Commercial paper
Due in one year or less	5,997		—		(6		)	5,991
Total short-term investments	$	148,432	$	449	$	(178	)	$	148,703
Long-term investments:
Auction rate securities
Due after five years	19,900		—		(2,373		)	17,527
Total long-term investments	$	19,900	$	—	$	(2,373	)	$	17,527
Total short and long-term investments	$	168,332	$	449	$	(2,551	)	$	166,230

Fair value of investments with unrealized losses

	June 30, 2012
	Less than 12 Months					12 Months or Greater					Total
	Fair		Unrealized			Fair		Unrealized			Fair		Unrealized
	Value		Losses			Value		Losses			Value		Losses
Corporate debt securities	$	58,433	$	(92	)	$	937	$	(15	)	$	59,370	$	(107	)
U.S. treasury and government agency securities	8,391		(4		)	—		—			8,391		(4		)
Commercial paper	7,477		(10		)	—		—			7,477		(10		)
	$	74,301	$	(106	)	$	937	$	(15	)	$	75,238	$	(121	)

	December 31, 2011
	Less than 12 Months					12 Months or Greater					Total
	Fair		Unrealized			Fair		Unrealized			Fair		Unrealized
	Value		Losses			Value		Losses			Value		Losses
Corporate debt securities	$	34,097	$	(161	)	$	4,124	$	(4	)	$	38,221	$	(165	)
U.S. treasury and government agency securities	8,841		(7		)	—		—			8,841		(7		)
Commercial paper	5,991		(6		)	—		—			5,991		(6		)
Auction rate securities	—		—			19,900		(2,373		)	19,900		(2,373		)
	$	48,929	$	(174	)	$	24,024	$	(2,377	)	$	72,953	$	(2,551	)