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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
Jun. 30, 2017
Class of Stock [Line Items]    
Unrecognized compensation expense $ 4,400,000  
Unrecognized compensation expense weighted average period 1 year 6 months  
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)
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