Nature of operations and summary of significant accounting policies (Property and Equipment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Accounting Policies [Abstract]
Impairment of other assets	$ 6,407	$ 0	$ 6,407	$ 0
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	52,487		52,487		$ 50,426
Less accumulated depreciation, amortization and impairment	21,341		21,341		12,449
Property and equipment, excluding land, net	31,146		31,146		37,977
Land	5,119		5,119		5,119
Property and equipment - at cost, net	36,265		36,265		43,096
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	520		520		520
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	4,712		4,712		3,548
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	21,832		21,832		21,482
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	6,685		6,685		6,183
Building and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, excluding land, gross	$ 18,738		$ 18,738		$ 18,693