Employee Stock Benefit Plans - Workforce Reduction (Details) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 07, 2019 employee	Apr. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Employee Stock Benefit Plans
Share-based compensation expense			$ 7,091	$ 6,337	$ 13,455	$ 20,271
Share-based Payment Awards, Excluding Employee Stock Purchase Plan
Employee Stock Benefit Plans
Share-based compensation expense		$ 0
Employee Stock Purchase Plan
Employee Stock Benefit Plans
Share-based compensation expense				300		300
Reduction in Workforce, February 7, 2019
Workforce Reduction
Number of employees expected to be eliminated | employee	35
Employee Stock Benefit Plans
Share-based compensation expense				$ 700		$ 700