Cash Equivalents - Summary of Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	$ 111,801	$ 21,680
Fair Value	111,801	21,680
Money Market Funds
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	111,801	21,680
Fair Value	$ 111,801	$ 21,680