CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) $ in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USN ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USN ($)
Depreciation and amortization	$ 6,594	$ 6,908	$ 20,378		$ 19,875
Stock-based compensation expense	1,077	1,225		$ 3,732		$ 3,265
Selling, general and administrative expenses
Depreciation and amortization	177	147	497		411
Stock-based compensation expense	1,011	1,139		3,356		3,042
System rental
Depreciation and amortization	6,052	5,773	18,087		16,481
Stock-based compensation expense	(14)	10		16		24
System services
Depreciation and amortization	172	384	803		1,173
Stock-based compensation expense	76	71		349		187
Transloading services
Depreciation and amortization	0	411	411		1,231
Stock-based compensation expense	4	5		$ 11		$ 12
Inventory software services
Depreciation and amortization	$ 193	$ 193	$ 579		$ 579