Investments (Tables)

12 Months Ended

Dec. 31, 2012

Investments

Summary of investments

The following is a summary of our investments as of December 31, 2012 and 2011 (in thousands):

	December 31, 2012
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate debt securities
Due in one year or less	$	52,332	$	88	$	(6	)	$	52,414
Due in one to three years		59,176		137		(37	)		59,276
U.S. treasury and government agency securities
Due in one year or less		24,795		86		—			24,881
Due in one to three years		34,606		84		(2	)		34,688
Commercial paper
Due in one year or less		9,494		1		(4	)		9,491
Total investments	$	180,403	$	396	$	(49	)	$	180,750

	December 31, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair 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 investments	$	168,332	$	449	$	(2,551	)	$	166,230

Summary of fair value of investments with unrealized losses

The following is a summary of the fair value of our investments with unrealized losses that are deemed to be temporarily impaired and their respective gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position as of December 31, 2012 and 2011 (in thousands):

	December 31, 2012
	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate debt securities	$	37,036	$	(43	)	$	—	$	—	$	37,036	$	(43	)
U.S. treasury and government agency securities		6,271		(2	)		—		—		6,271		(2	)
Commercial paper		3,992		(4	)		—		—		3,992		(4	)
	$	47,299	$	(49	)	$	—	$	—	$	47,299	$	(49	)

	December 31, 2011
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized 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	)