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Discontinued Operations, Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2019
Dec. 31, 2019
Identifiable intangible assets with finite useful lives    
Intangible Assets, Net $ 99,636 $ 94,274
Backlog and customer relationships    
Identifiable intangible assets with finite useful lives    
Gross Amount 661,400 662,200
Accumulated Amortization (561,800) (567,900)
Intangible Assets, Net $ 99,600 $ 94,300
Backlog and customer relationships | Minimum    
Identifiable intangible assets with finite useful lives    
Amortization Period 1 year  
Backlog and customer relationships | Maximum    
Identifiable intangible assets with finite useful lives    
Amortization Period 11 years