Income tax (expense) benefit - Deferred income taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 91,995	$ 70,871
Tax loss on liquidation of subsidiary	6,245	7,846
Equity compensation	2,473	1,450
Non-deductible reserves	203	57
Total deferred tax assets	100,916	80,224
Valuation allowance	(100,832)	(80,087)	$ (54,114)	$ (40,487)
Net deferred tax assets	84	137
Deferred tax liabilities:
Financial liabilities	55	80
Property, plant and equipment	29	57
Total deferred tax liability	84	137
Deferred tax, net	$ 0	$ 0