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Revenue Recognition (Disaggregated Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 77,739	$ 66,032
Services provided or goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	1,023	1,077
Recurring term contracts: Primary Term
Disaggregation of Revenue [Line Items]
Total revenues	42,997	36,626
Recurring term contracts: Month-to-month
Disaggregation of Revenue [Line Items]
Total revenues	33,719	23,806
Non-recurring term contracts: Station installations
Disaggregation of Revenue [Line Items]
Total revenues		4,523
Contract operations revenue
Disaggregation of Revenue [Line Items]
Total revenues	76,716	60,432
Retail parts and services revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,023	1,077
Station installations revenue
Disaggregation of Revenue [Line Items]
Total revenues		$ 4,523

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+ References

No definition available.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
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-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

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