Commitment and Contingencies - Lease Narrative (Details) $ in Thousands			1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 24, 2018	Jul. 18, 2018 USD ($) ft²	Apr. 30, 2016 USD ($)	Mar. 31, 2016 ft²	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)
Lease Description [Line Items]
Operating lease cost					$ 1,600	$ 1,600	$ 3,200	$ 3,200
Total cash paid against operating lease liability					$ 1,500	1,400	$ 3,000	2,900
Operating lease (area) | ft²				128,751
Operating lease, weighted average remaining lease term					3 years 6 months		3 years 6 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, non-current					$ 2,704	2,704	$ 2,704	2,704		$ 2,704
Area of sub-sublease rental | ft²		46,641
Sublease income					700	$ 700	1,500	$ 1,500
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%