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Intangible Asset - Schedule of Carrying Value of Intangible Asset (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]    
Technology rights $ 11,624 $ 11,624
Accumulated amortization (4,467) (4,144)
Intangible assets, net $ 7,157 $ 7,480