Assets - Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Short-term investments
Transfer of assets from Level 1 to Level 2	$ 0
Transfer of assets from Level 2 to Level 1	0
Transfer of Liabilities from Level 1 to Level 2	0
Transfer of Liabilities from Level 2 to Level 1	0
Measured at fair value on a recurring basis
Cash equivalents
Total Cash equivalents	76,875	$ 78,493
Short-term investments
Total Short-term investments	161,585	115,252
Measured at fair value on a recurring basis | U.S. treasuries
Short-term investments
Total Short-term investments	125,346	105,130
Measured at fair value on a recurring basis | Government agency securities
Short-term investments
Total Short-term investments	6,000	1,139
Measured at fair value on a recurring basis | Corporate debt
Short-term investments
Total Short-term investments	14,248	6,002
Measured at fair value on a recurring basis | Commercial paper
Short-term investments
Total Short-term investments	15,991	2,981
Measured at fair value on a recurring basis | Certificate of deposits and time deposits
Cash equivalents
Total Cash equivalents	64,646	67,009
Measured at fair value on a recurring basis | U.S. treasuries
Cash equivalents
Total Cash equivalents	9,999
Measured at fair value on a recurring basis | Government money market fund
Cash equivalents
Total Cash equivalents	1,180
Measured at fair value on a recurring basis | Government agency securities
Cash equivalents
Total Cash equivalents	1,050
Measured at fair value on a recurring basis | Commercial paper
Cash equivalents
Total Cash equivalents		10,484
Measured at fair value on a recurring basis | Corporate debt
Cash equivalents
Total Cash equivalents		1,000
Measured at fair value on a recurring basis | Level 1
Cash equivalents
Total Cash equivalents	75,825	67,009
Short-term investments
Total Short-term investments	125,346	105,130
Measured at fair value on a recurring basis | Level 1 | U.S. treasuries
Short-term investments
Total Short-term investments	125,346	105,130
Measured at fair value on a recurring basis | Level 1 | Certificate of deposits and time deposits
Cash equivalents
Total Cash equivalents	64,646	67,009
Measured at fair value on a recurring basis | Level 1 | U.S. treasuries
Cash equivalents
Total Cash equivalents	9,999
Measured at fair value on a recurring basis | Level 1 | Government money market fund
Cash equivalents
Total Cash equivalents	1,180
Measured at fair value on a recurring basis | Level 2
Cash equivalents
Total Cash equivalents	1,050	11,484
Short-term investments
Total Short-term investments	36,239	10,122
Measured at fair value on a recurring basis | Level 2 | Government agency securities
Short-term investments
Total Short-term investments	6,000	1,139
Measured at fair value on a recurring basis | Level 2 | Corporate debt
Short-term investments
Total Short-term investments	14,248	6,002
Measured at fair value on a recurring basis | Level 2 | Commercial paper
Short-term investments
Total Short-term investments	15,991	2,981
Measured at fair value on a recurring basis | Level 2 | Government agency securities
Cash equivalents
Total Cash equivalents	$ 1,050
Measured at fair value on a recurring basis | Level 2 | Commercial paper
Cash equivalents
Total Cash equivalents		10,484
Measured at fair value on a recurring basis | Level 2 | Corporate debt
Cash equivalents
Total Cash equivalents		$ 1,000