Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Summary of fair value for assets measured on recurring basis

	Fair Value Measurements at Reporting Date Using
As of March 31, 2015	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents:
Money market funds	$	50,369	$	50,369	$	—
Total cash equivalents	50,369		50,369		—
Marketable securities:
U.S. treasury securities	30,026		30,026		—
Certificates of deposit	49		—		49
Mutual funds	543		543		—
Total marketable securities	30,618		30,569		49
Total	$	80,987	$	80,938	$	49

	Fair Value Measurements at Reporting Date Using
As of December 31, 2014	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents:
Money market funds	$	50,359	$	50,359	$	—
Total cash equivalents	50,359		50,359		—
Marketable securities:
U.S. treasury securities	30,020		30,020		—
Certificates of deposit	48		—		48
Mutual funds	520		520		—
Total marketable securities	30,588		30,540		48
Total	$	80,947	$	80,899	$	48

Carrying amounts and fair value of long-term obligations

	March 31, 2015				December 31, 2014
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Convertible Senior Notes	$	130,000	$	137,556	$	130,000	$	134,227