Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		$ 0
Fair Value Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	$ 140,755,000	57,032,000
Contingent consideration	682,000	388,000
Total financial liabilities	682,000	388,000
Fair Value Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	35,521,000	57,032,000
Fair Value Measurements, Recurring | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	11,974,000
Short-term investments	12,972,000
Fair Value Measurements, Recurring | U.S. Government and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	50,352,000
Short-term investments	29,936,000
Fair Value Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	35,521,000	57,032,000
Fair Value Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	35,521,000	57,032,000
Fair Value Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	105,234,000
Fair Value Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	11,974,000
Short-term investments	12,972,000
Fair Value Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	50,352,000
Short-term investments	29,936,000
Fair Value Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration	682,000	388,000
Total financial liabilities	$ 682,000	$ 388,000