Long-term debt (Details) $ in Thousands		6 Months Ended
	Mar. 21, 2017 USD ($) item	Jun. 30, 2017 USD ($)
Long-term debt
Amount drawn		$ 2,386
Term loan
Long-term debt
Maximum borrowing capacity	$ 25,000
Number of separate advances | item	4
Amount drawn	$ 2,500
Interest rate	10.50%	10.50%
Basis spread	(4.50%)
Minimum cash proceeds to extend interest only payment period	$ 20,000
Amortization payments, installments | item	26
Future principal payments
2018		$ 146
2019		936
2020		1,418
Total		$ 2,500
Term loan | Interest-only payments extended
Long-term debt
Amortization payments, installments | item	20
Term loan | Minimum
Long-term debt
Interest rate	10.50%
Term loan | Maximum
Long-term debt
Interest rate	12.75%