Fair Value Measurement (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
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
U.S. Treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	3,897
U.S. Treasuries | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	3,897
Recurring basis
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	84,948	96,770
Recurring basis | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	43,930	36,617
Recurring basis | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	41,018	60,153
Recurring basis | Money market funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	43,930	36,617
Recurring basis | Money market funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	43,930	36,617
Recurring basis | Corporate debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	930	6,555
Recurring basis | Corporate debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	930	6,555
Recurring basis | Commercial paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	36,191	53,598
Recurring basis | Commercial paper | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	$ 36,191	$ 53,598