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Senior Secured Notes (Detail) - USD ($)
12 Months Ended
Apr. 13, 2020
Oct. 05, 2015
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Secured Notes [Line Items]          
Principal amount repaid     $ 250,000,000 $ 0 $ 0
Senior Notes | 7.75% Senior Secured Notes Due October 2020          
Secured Notes [Line Items]          
Senior secured notes, principal amount   $ 250,000,000.0      
Senior secured notes, interest rate   7.75%      
Issuance costs   $ 8,900,000      
Debt discount on transaction and facility fees   $ 8,700,000      
Principal amount repaid $ 250,000,000.0        
Interest Receivable $ 4,800,000