Restructuring Charge (Details) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) ft²	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Restructuring charge
Restructuring charge	$ 1,020			$ 1,524	$ 20,921
Workforce reduction
Restructuring charge
Balance at beginning of the period				4,087
Additional charges/adjustments during the period				(116)
Payments during the period				(2,859)
Balance at end of the period			$ 4,087	1,112		$ 4,087
Workforce reduction | 2019 Corporate Restructuring
Restructuring
Charge for severance related to a pre-existing plan		$ 16,000
Costs incurred			$ 15,300
Incremental retention benefits | 2019 Corporate Restructuring
Restructuring
Costs incurred		$ 4,000		$ 1,600		$ 2,400
Winter Street 930 Waltham MA
Restructuring charge
Unoccupied office space for sub-lease | ft²				10,281
Leasehold impairment charge					$ 600