Fair Value Measurements and Investments in Marketable Securities - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - Money Market Funds - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Assets measured at fair value	$ 40,026	$ 89,965
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Assets measured at fair value	$ 40,026	$ 89,965