Summary of Significant Accounting Policies - Intangibles (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 06, 2017
Intangible assets by major classification
Intangible assets, net	$ 5,335	$ 36
2018	770
2019	770
2020	770
2021	770
2022	770
Intangible amortization expense	46	1	$ 0
Gross	5,382	37
Accumulated Amortization	(47)	(1)
Net Book Value	5,335	36
Goodwill	17,236	13,004
Goodwill impairment	0	0	$ 0
Patents and other
Intangible assets by major classification
Gross	108	37
Accumulated Amortization	(5)	(1)
Net Book Value	103	$ 36
Customer relationships
Intangible assets by major classification
Gross	4,703
Accumulated Amortization	(36)
Net Book Value	4,667
Computer software
Intangible assets by major classification
Gross	346
Accumulated Amortization	(3)
Net Book Value	343
Non-competition agreement
Intangible assets by major classification
Gross	225
Accumulated Amortization	(3)
Net Book Value	$ 222
Minimum
Intangible assets by major classification
Definite-lived intangible assets useful life	5 years
Maximum
Intangible assets by major classification
Definite-lived intangible assets useful life	15 years
Railtronix LLC
Intangible assets by major classification
Goodwill				$ 4,237