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Schedule of Outstanding Debt (Detail) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]    
Secured long-term debt $ 378,696 $ 281,625
Less current portion (94,620) (94,691)
Total long-term debt 284,076 186,934
Secured Equipment Notes due in 2025 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 21,444  
Secured Equipment Notes due in 2024 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 59,517 62,690
Secured Equipment Notes due in 2023 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 143,445 153,350
Secured Equipment Notes due in 2022 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 14,546 16,892
Secured Equipment Notes due in 2021 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 30,142 35,076
Secured Equipment Notes due in 2020 [Member]    
Debt Instrument [Line Items]    
Secured long-term debt 9,602 $ 13,617
Revolving Line of Credit Facility [Member]    
Debt Instrument [Line Items]    
Borrowings on revolving line of credit $ 100,000