Accounts payable and Accrued Liabilities - Additional Information (Detail) - Vendor	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts Payable And Accrued Expenses [Line Items]
Number of vendors	3	2
Accounts Payable [Member] | Supplier Concentration Risk [Member]
Accounts Payable And Accrued Expenses [Line Items]
Percentage of amount due to major vendors accounts payable	39.00%	28.00%