Fair Value Measurement (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Financial and nonfinancial liabilities measured at fair value	$ 0	$ 0
Nonfinancial assets measured at fair value	0	0
Total	71,697	69,455
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	14,443	10,583
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	57,254	58,872
Money market funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	14,443	10,583
Money market funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	14,443	10,583
Corporate debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	6,145	7,076
Corporate debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	6,145	7,076
Commercial paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	49,609	51,796
Commercial paper | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	49,609	$ 51,796
Certificates of deposit
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	1,500
Certificates of deposit | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	$ 1,500