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Leases - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 12 Months Ended
Jun. 30, 2018
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Leases [Line Items]        
Amortization of deferred airborne lease incentives   $ 7,630 $ 9,348  
Deferred airborne lease incentives included in current liabilities   29,472   $ 42,096
Deferred airborne lease incentives included in non-current liabilities   124,653   142,938
Revenue share expense, net of amortization of deferred airborne lease incentives   6,400 8,900  
Property and equipment, gross   882,703   1,053,923
Present value of net minimum lease payments   2,296    
Present value of net minimum lease payments, current portion   1,468   1,789
Present value of net minimum lease payments, non-current portion   800    
Scenario, Forecast [Member]        
Leases [Line Items]        
Contingent annual cash rebate $ 1,800      
Leased Computer Equipment [Member]        
Leases [Line Items]        
Property and equipment, gross   5,000   5,000
Leased Network Equipment [Member]        
Leases [Line Items]        
Property and equipment, gross   7,500   $ 7,500
Certain Facilities and Equipment [Member]        
Leases [Line Items]        
Rental expense   3,100 3,000  
Cell Site Leases [Member]        
Leases [Line Items]        
Rental expense   $ 2,700 $ 2,300  
Minimum [Member] | Computer Equipment [Member]        
Leases [Line Items]        
Annual interest rate imputed   8.00%    
Maximum [Member] | Computer Equipment [Member]        
Leases [Line Items]        
Annual interest rate imputed       14.00%