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Fair Value measurements - Summary of Carrying Values and Associated Fair Values of Financial Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Carrying Value [Member]    
Financial assets:    
Investments $ 9,923 $ 10,060
Level 2 [Member]    
Financial assets:    
Investments $ 9,928 $ 10,053