Significant Tenant - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 28, 2019 ft²
Real Estate Properties [Line Items]
Rental revenues	$ 57,760	$ 59,125	$ 170,470	$ 175,258
Customer Concentration Risk | Revenue
Real Estate Properties [Line Items]
Percentage of minimum revenue threshold contributed by one tenant			10.00%
Bloomberg | Customer Concentration Risk | Revenue
Real Estate Properties [Line Items]
Percentage rent contributed by tenant			48.00%	46.00%
Real Estate | Bloomberg | Customer Concentration Risk | Revenue
Real Estate Properties [Line Items]
Rental revenues			$ 81,314	$ 80,024
731 Lexington Avenue | Bloomberg
Real Estate Properties [Line Items]
Area of property (in sqft.) | ft²					49,000