Summary of Significant Accounting Policies - Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair value hierarchy for the Company's financial assets measured at fair value
Interest rate (as a percent)	4.50%	4.50%
Convertible Notes
Fair value hierarchy for the Company's financial assets measured at fair value
Interest rate (as a percent)	4.50%		4.50%	4.50%
Principal amount of debt for conversion calculations	$ 1,000			$ 1,000
Significant Other Observable Inputs (Level 2) | Convertible Notes | Face Value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value	2,100,000	$ 2,100,000
Significant Other Observable Inputs (Level 2) | Convertible Notes | Estimated fair value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value	3,000,000.0	2,800,000
Recurring basis
Fair value hierarchy for the Company's financial assets measured at fair value
Cash equivalents	163,674,000	242,604,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value hierarchy for the Company's financial assets measured at fair value
Cash equivalents	$ 163,674,000	$ 242,604,000