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Subsequent events - Additional Information (Detail) - Subsequent Event
1 Months Ended
Nov. 01, 2018
USD ($)
ft²
Dec. 17, 2018
$ / shares
Subsequent Event [Line Items]    
Dividends payable, amount per share | $ / shares   $ 0.02
Dividends payable, date to be paid   Jan. 15, 2019
Dividends payable, record date   Dec. 31, 2018
Area of Land | ft² 7,500  
Operating Leases, Rent Expense | $ $ 5,625  
Lease Expiration Date Oct. 31, 2019