Commitment and Contingencies - Lease Narrative (Details) $ in Thousands			1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 24, 2018	Jul. 18, 2018 USD ($) ft²	Dec. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Mar. 31, 2016 ft²	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Lease Description [Line Items]
Operating lease cost						$ 1,600	$ 1,600	$ 4,800	$ 4,800
Total cash paid against operating lease liability						$ 1,500	1,500	$ 4,500	4,300
Operating lease (area) | ft²					128,751
Operating lease, weighted average remaining lease term						3 years 3 months		3 years 3 months
Operating lease, current SSF facility, term of contract					7 years 9 months 30 days
Lease expiration date					Dec. 31, 2023
Total lease payments due over lease term				$ 39,200
Tenant improvement allowance			$ 14,200
Restricted cash						$ 2,700		$ 2,700
Area of sub-sublease rental | ft²		46,641
Sublease income						700	$ 700	2,200	$ 2,200
Sub-sublease rentals, initial annual base rent		$ 2,700
Sub-sublease rentals, percent annual rent increase		3.50%
Sub-sublease rentals, term of contract	5 years 2 months 12 days
Sub-sublease rentals, percent of rental gain attributable to sublandlord		50.00%
Current SSF Facility operating lease under ASC 842
Lease Description [Line Items]
Line of credit facility				4,100
Face amount reduction on third anniversary				1,400
Face amount reduction on fifth anniversary				$ 1,400
Line of credit has been used						$ 0		$ 0
ASC-842
Lease Description [Line Items]
Discount rate, percent						4.25%		4.25%