Income tax expense - Deferred Income Tax (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 94,014	$ 91,995
Tax loss on liquidation of subsidiary	5,024	6,245
Equity compensation	4,182	2,473
Non-deductible reserves	395	203
Total deferred tax assets	103,615	100,916
Valuation allowance	(103,185)	(100,832)	$ (80,087)	$ (54,114)
Net deferred tax assets	430	84
Deferred tax liabilities:
Financial liabilities	48	55
Property, plant and equipment	382	29
Total deferred tax liability	430	84
Deferred tax, net	$ 0	$ 0