Summary of Significant Accounting Policies - Basis of Presentation, Credit Risk and Income Taxes (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2019 USD ($)	Mar. 31, 2020 USD ($) segment item	Dec. 31, 2019 USD ($)
Accumulated deficit		$ (230,080)	$ (217,145)
Cash, cash equivalents and marketable securities		$ 68,700
Concentrations of Credit Risk and Other Risks and Uncertainties
Number of financial institutions used for cash and cash equivalent deposits | item		2
Segments
Number of operating segments | segment		1
Recent accounting pronouncements
Package of practical expedients adopted	true
Use of hindsight adopted	false
Operating lease right-of-use asset		$ 2,163	2,327
Operating lease liabilities		$ 2,977	$ 3,188
ASU 2016-02
Recent accounting pronouncements
Operating lease right-of-use asset	$ 2,800
Operating lease liabilities	3,800
Deferred rent	$ 1,000