Long-term Debt - Summary of Long-term Debt (Parenthetical) (Detail) - Mortgage Loan Payable [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt instrument interest rate	11.50%	11.50%	11.50%
Debt instrument maturity period	Jan. 31, 2019	Jan. 31, 2019