Annual report pursuant to Section 13 and 15(d)

Acquisitions Acquisitions - Schedule of Assets Acquired and Liabilities Assumed Air Rescue Systems and Brim Equipment Assets (Details)

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Acquisitions Acquisitions - Schedule of Assets Acquired and Liabilities Assumed Air Rescue Systems and Brim Equipment Assets (Details) - USD ($)
$ in Thousands
Dec. 21, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Business Acquisition [Line Items]        
Goodwill   $ 101,245 $ 99,811 $ 88,727
Cobra Aviation Services LLC | ARS        
Business Acquisition [Line Items]        
Accounts receivable $ 146      
Property, plant and equipment 1,702      
Identifiable intangible assets 120      
Goodwill 694      
Other assets 5      
Total assets acquired $ 2,667      
Acquired finite-lived intangible assets, weighted average useful life (in years) 20 years      
Cobra Aviation Services LLC | Brim Equipment Assets        
Business Acquisition [Line Items]        
Accounts receivable $ 0      
Property, plant and equipment 1,990      
Identifiable intangible assets 0      
Goodwill 2,243      
Other assets 0      
Total assets acquired $ 4,233