Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Company’s assets that were accounted for at fair value on a recurring basis
Short-term investments	$ 33,509	$ 35,732
Recurring
Company’s assets that were accounted for at fair value on a recurring basis
Total	46,655	74,305
Recurring | Level 1
Company’s assets that were accounted for at fair value on a recurring basis
Total	40,561	68,246
Recurring | Level 2
Company’s assets that were accounted for at fair value on a recurring basis
Total	6,094	6,059
Recurring | Money market funds
Company’s assets that were accounted for at fair value on a recurring basis
Cash equivalents	13,146	18,609
Recurring | Money market funds | Level 1
Company’s assets that were accounted for at fair value on a recurring basis
Cash equivalents	13,146	18,609
Recurring | U.S. Treasury securities
Company’s assets that were accounted for at fair value on a recurring basis
Cash equivalents		19,964
Short-term investments	27,415	29,673
Recurring | U.S. Treasury securities | Level 1
Company’s assets that were accounted for at fair value on a recurring basis
Cash equivalents		19,964
Short-term investments	27,415	29,673
Recurring | U.S. government-sponsored enterprise securities
Company’s assets that were accounted for at fair value on a recurring basis
Short-term investments	6,094	6,059
Recurring | U.S. government-sponsored enterprise securities | Level 2
Company’s assets that were accounted for at fair value on a recurring basis
Short-term investments	$ 6,094	$ 6,059