Quarterly report pursuant to Section 13 or 15(d)

Intangible Assets (Details)

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Intangible Assets (Details) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Schedule Of Intangible Assets [Line Items]    
Intangible assets subject to amortization, Gross Carrying Amount $ 123,368 $ 124,028
Intangible assets subject to amortization, Accumulated Amortization (88,077) (69,127)
Intangible assets subject to amortization, Net Carrying Amount 35,291 54,901
Customer relationships    
Schedule Of Intangible Assets [Line Items]    
Intangible assets subject to amortization, Gross Carrying Amount 120,000 120,000
Intangible assets subject to amortization, Accumulated Amortization (85,533) (66,866)
Intangible assets subject to amortization, Net Carrying Amount $ 34,467 $ 53,134
Weighted- Average Amortization Period (Years) 6 years 6 years
Licenses    
Schedule Of Intangible Assets [Line Items]    
Intangible assets subject to amortization, Gross Carrying Amount $ 3,368 $ 3,368
Intangible assets subject to amortization, Accumulated Amortization (2,544) (1,601)
Intangible assets subject to amortization, Net Carrying Amount $ 824 $ 1,767
Weighted- Average Amortization Period (Years) 5 years 7 months 6 days 5 years 7 months 6 days
Non-compete agreements    
Schedule Of Intangible Assets [Line Items]    
Intangible assets subject to amortization, Gross Carrying Amount   $ 660
Intangible assets subject to amortization, Accumulated Amortization   (660)
Intangible assets subject to amortization, Net Carrying Amount   $ 0
Weighted- Average Amortization Period (Years)   1 year