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Asset Disposals - Additional Information (Detail)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Aircraft
Jun. 30, 2018
Aircraft
Mar. 31, 2018
Aircraft
Sep. 30, 2017
Aircraft
Jun. 30, 2017
Aircraft
Mar. 31, 2017
Aircraft
Sep. 30, 2018
USD ($)
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft sold           0  
Cash realized from sale of assets | $             $ 1.5
Gain (loss) on disposal of assets | $             $ 0.7
Medium Aircraft [Member]              
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft sold         5    
Air Medical [Member] | Light Aircraft [Member]              
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft sold     1        
Oil and Gas [Member]              
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft donated     1        
Oil and Gas [Member] | Light Aircraft [Member]              
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft sold   1          
Oil and Gas [Member] | Medium Aircraft [Member]              
Assets Held For Sale And Impairments [Line Items]              
Number of aircraft sold 1 1   1