Fair Value Measurements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Summary of financial instruments measured at fair value on a recurring basis
Non-marketable debt security	$ 1,289,000		$ 1,289,000		$ 1,000,000
Total	112,372,000		112,372,000		128,567,000
Convertible Debt
Summary of financial instruments measured at fair value on a recurring basis
Credit losses	0	$ 0	0	$ 0
Other-than-temporary impairment losses	0	$ 0	0	$ 0
Money Market Funds
Summary of financial instruments measured at fair value on a recurring basis
Money market funds	111,083,000		111,083,000		127,567,000
Level 1
Summary of financial instruments measured at fair value on a recurring basis
Total	111,083,000		111,083,000		127,567,000
Level 1 | Money Market Funds
Summary of financial instruments measured at fair value on a recurring basis
Money market funds	111,083,000		111,083,000		127,567,000
Level 3
Summary of financial instruments measured at fair value on a recurring basis
Non-marketable debt security	1,289,000		1,289,000		1,000,000
Total	$ 1,289,000		$ 1,289,000		$ 1,000,000