Financial Instruments and Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurements
Assets at fair value	$ 177,580	$ 251,618
Money market
Fair Value Measurements
Assets at fair value	112,529	61,882
U.S. treasury securities
Fair Value Measurements
Assets at fair value	65,051	189,736
Fair Value, Inputs, Level 1
Fair Value Measurements
Assets at fair value	112,529	116,792
Fair Value, Inputs, Level 1 | Money market
Fair Value Measurements
Assets at fair value	112,529	61,882
Fair Value, Inputs, Level 1 | U.S. treasury securities
Fair Value Measurements
Assets at fair value		54,910
Fair Value, Inputs, Level 2
Fair Value Measurements
Assets at fair value	65,051	134,826
Fair Value, Inputs, Level 2 | Money market
Fair Value Measurements
Assets at fair value	0	0
Fair Value, Inputs, Level 2 | U.S. treasury securities
Fair Value Measurements
Assets at fair value	65,051	134,826
Fair Value, Inputs, Level 3
Fair Value Measurements
Assets at fair value	0	0
Fair Value, Inputs, Level 3 | Money market
Fair Value Measurements
Assets at fair value	0	0
Fair Value, Inputs, Level 3 | U.S. treasury securities
Fair Value Measurements
Assets at fair value	$ 0	$ 0