Leases - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Feb. 29, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Aggregate lease payments	$ 15,364			$ 14,899
Cash paid for amounts included in measurement of lease liabilities	1,000	$ 600
Right-of-use asset obtained in exchange for new operating lease liabilities	$ 1,200
Weighted average remaining lease term	6 years 6 months
Weighted-average discount rate (percent)	6.20%
Maidenhead, United Kingdom lease
Lessee, Lease, Description [Line Items]
Term of new lease			5 years
Aggregate lease payments			$ 1,500