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Share-Based Payment Awards - Stock-Based Compensation Expense - Additional Information (Detail) - USD ($)
 6 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2019
Jun. 30, 2017
Class of Stock [Line Items]      
Amount of stock-based compensation attributable to accelerated vesting and extension of option exercise period of certain stock options, net of non-vested option forfeitures     $ (104,000)
Unrecognized compensation expense   $ 4,100,000  
Unrecognized compensation expense weighted average period   1 year 5 months 12 days  
General and Administrative Expense [Member]      
Class of Stock [Line Items]      
Amount of stock-based compensation attributable to accelerated vesting and extension of option exercise period of certain stock options, net of non-vested option forfeitures     274,000
Research and Development Expense [Member] | UNITED KINGDOM      
Class of Stock [Line Items]      
Amount of stock-based compensation attributable to extension of option exercise period of vested options and forfeiture of all non-vested stock options in connection with U.K. restructuring     $ (35,000)
Selling and Marketing Expense [Member]      
Class of Stock [Line Items]      
Amount of stock-based compensation attributable to accelerated vesting, net of non-vested option forfeitures $ 171,000