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Accretion of Debt Issuance Cost and Debt Discount (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Debt Disclosure [Abstract]    
Accretion expense - debt issuance cost $ 14 $ 6
Accretion expense - debt discount $ 72 $ 310