Fair Value Measurements - Summary of Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Short-term marketable securities	$ 115,949	$ 155,736
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	33,239	14,131
Short-term marketable securities	115,949	155,736
Total assets subject to fair value measurements on a recurring basis	149,188	169,867
Liabilities:
Total liabilities subject to fair value measurements on a recurring basis	1,238	2,483
Fair Value, Measurements, Recurring | Contingent Consideration Liability
Liabilities:
Total liabilities subject to fair value measurements on a recurring basis	1,238	2,483
Fair Value, Measurements, Recurring | Level 1
Assets:
Cash equivalents	33,239	14,131
Total assets subject to fair value measurements on a recurring basis	33,239	14,131
Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities	115,949	155,736
Total assets subject to fair value measurements on a recurring basis	115,949	155,736
Fair Value, Measurements, Recurring | Level 3
Liabilities:
Total liabilities subject to fair value measurements on a recurring basis	1,238	2,483
Fair Value, Measurements, Recurring | Level 3 | Contingent Consideration Liability
Liabilities:
Total liabilities subject to fair value measurements on a recurring basis	1,238	2,483
Money market funds | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	29,239	14,131
Money market funds | Fair Value, Measurements, Recurring | Level 1
Assets:
Cash equivalents	29,239	14,131
Receivable From Maturity Of U.S. Treasury Security | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	4,000
Receivable From Maturity Of U.S. Treasury Security | Fair Value, Measurements, Recurring | Level 1
Assets:
Cash equivalents	4,000
US Government Debt Securities | Fair Value, Measurements, Recurring
Assets:
Short-term marketable securities	65,721	81,699
US Government Debt Securities | Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities	65,721	81,699
US Treasury Securities | Fair Value, Measurements, Recurring
Assets:
Short-term marketable securities	17,204	34,121
US Treasury Securities | Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities	17,204	34,121
U.S. and Foreign Commercial Paper | Fair Value, Measurements, Recurring
Assets:
Short-term marketable securities	16,616	10,635
U.S. and Foreign Commercial Paper | Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities	16,616	10,635
Corporate Debt Securities | Fair Value, Measurements, Recurring
Assets:
Short-term marketable securities	16,408	26,533
Corporate Debt Securities | Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities	$ 16,408	26,533
Asset-backed Securities | Fair Value, Measurements, Recurring
Assets:
Short-term marketable securities		2,748
Asset-backed Securities | Fair Value, Measurements, Recurring | Level 2
Assets:
Short-term marketable securities		$ 2,748