CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) $ in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USN ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USN ($)
Depreciation and amortization	$ 6,671	$ 6,622	$ 13,785		$ 12,967
Stock-based compensation expense	1,326	1,178		$ 2,656		$ 2,040
Selling, general and administrative expenses
Depreciation and amortization	172	146	324		265
Stock-based compensation expense	1,231	1,112		2,345		1,903
System rental
Depreciation and amortization	6,034	5,481	12,035		10,707
Stock-based compensation expense	18	10		31		14
System services
Depreciation and amortization	274	391	631		789
Stock-based compensation expense	73	52		273		116
Transloading services
Depreciation and amortization	0	411	411		820
Stock-based compensation expense	4	4		$ 7		$ 7
Inventory software services
Depreciation and amortization	$ 191	$ 193	$ 384		$ 386