Fair Value Measurement (Details) - Fair value measurement, Recurring - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurement
Asset at fair value	$ 14,749,000	$ 29,075,000
Liabilities at fair value	0	0
Money market funds
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 1
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 1 | Money market funds
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 2
Fair Value Measurement
Asset at fair value	0	0
Level 2 | Money market funds
Fair Value Measurement
Asset at fair value	0	0
Level 3
Fair Value Measurement
Asset at fair value	0	0
Level 3 | Money market funds
Fair Value Measurement
Asset at fair value	$ 0	$ 0