Investments and Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2012

Investments and Fair Value Measurement [Abstract]

Schedule of available-for-sale securities

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
September 30, 2012
Cash equivalents:
Money market funds	$	13,595	$	—	$	—	$	13,595
Total		13,595		—		—		13,595
Marketable securities:
U.S. government sponsored entity debt securities		42,732		15		—		42,747
Corporate debt securities		19,345		—		—		19,345
Total		62,077		15		—		62,092
Total cash equivalents and marketable securities	$	75,672	$	15	$	—	$	75,687

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
December 31, 2011
Cash equivalents:
Money market funds	$	15,258	$	—	$	—		$	15,258
Total		15,258		—		—			15,258
Marketable securities:
U.S. government sponsored entity debt securities		27,020		—		(7	)		27,013
U.S. treasury debt securities		751		1		—			752
Corporate debt securities		39,583		18		—			39,601
Total		67,354		19		(7	)		67,366
Total cash equivalents and marketable securities	$	82,612	$	19	$	(7	)	$	82,624

Summary of fair value measurements of cash equivalents and available-for-sale marketable securities

	September 30, 2012 Fair Value Measurements
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	13,595	$	13,595	$	—	$	—
Total		13,595		13,595		—		—
Marketable securities:
U.S. government sponsored entity debt securities		42,747		—		42,747		—
Corporate debt securities		19,345		—		19,345		—
Total		62,092		—		62,092		—
Total cash equivalents and marketable securities	$	75,687	$	13,595	$	62,092	$	—

	December 31, 2011 Fair Value Measurements
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	15,258	$	15,258	$	—	$	—
Total		15,258		15,258		—		—
Marketable securities:
U.S. government sponsored entity debt securities		27,013		—		27,013		—
U.S. treasury debt securities		752		—		752		—
Corporate debt securities		39,601		—		39,601		—
Total		67,366		—		67,366		—
Total cash equivalents and marketable securities	$	82,624	$	15,258	$	67,366	$	—