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Schedule of Amortization of Premium and Accretion of Debt Issuance Costs (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Debt Instrument [Line Items]    
Amortization of debt premium $ 72 $ 310
2021 Notes    
Debt Instrument [Line Items]    
Amortization of debt premium 36 $ 43
Accretion expense - debt issuance cost $ 2