Debt (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 01, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt instruments
Amount borrowed			$ 500		$ 500
Interest expense			$ 2,180	$ 432	$ 6,335	$ 1,214
2014 Debt Facility
Debt instruments
Interest-only end date extension period		12 months
Unpaid principal balance				20,000		20,000
Unamortized discount				200		200
Interest expense				$ 400		1,200
Amortization of debt discount						100
Contractual coupon interest						$ 1,100
Debt repayments	$ 20,000
Prepayment fees paid	$ 200