Fair Value Measurements - Assets measured at fair value on a recurring basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Available-for-sale Securities
Total	$ 46,322	$ 46,174
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds (included in cash and cash equivalents)
Schedule of Available-for-sale Securities
Money market funds (included in cash and cash equivalents)	46,322	46,174
Significant Other Observable Inputs (Level 2)
Schedule of Available-for-sale Securities
Total	0	0
Significant Other Observable Inputs (Level 2) | Money market funds (included in cash and cash equivalents)
Schedule of Available-for-sale Securities
Money market funds (included in cash and cash equivalents)	0	0
Significant Unobservable Inputs (Level 3)
Schedule of Available-for-sale Securities
Total	0	0
Significant Unobservable Inputs (Level 3) | Money market funds (included in cash and cash equivalents)
Schedule of Available-for-sale Securities
Money market funds (included in cash and cash equivalents)	$ 0	$ 0