Shareholders' Equity, Noncontrolling Interests and Other Comprehensive Income - Preferred OP Units - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended		33 Months Ended	237 Months Ended
	Sep. 30, 2018	Dec. 31, 2016	Dec. 31, 1999	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Denominator for Series A Preferred OP Unit conversion	$ 7,500			$ 7,500	$ 7,500
Gotham Plaza | Common Shares
Class of Stock [Line Items]
Issuance of common shares, net of issuance costs (in Shares)		442,478
Preferred quarterly distribution per share price		$ 0.9375
Number of convertible units if share price below $28.80 (in shares)		3.4722
Number of convertible units if share price above $35.20 (in shares)		2.8409
Operating Partnership, as General Partner or Managing Member
Class of Stock [Line Items]
Series A Preferred OP Units (in shares)	3,331,440			3,331,440	3,331,440	3,328,873
Preferred OP Units
Class of Stock [Line Items]
Issuance of common shares, net of issuance costs (in Shares)	0
Preferred OP Units | Gotham Plaza
Class of Stock [Line Items]
Issuance of common shares, net of issuance costs (in Shares)		141,593
Share price (in dollars per share)		$ 100.00
Preferred OP Units | Gotham Plaza | Minimum
Class of Stock [Line Items]
Share price at conversion date		28.80
Preferred OP Units | Gotham Plaza | Maximum
Class of Stock [Line Items]
Share price at conversion date		$ 35.20
Series A Preferred Stock
Class of Stock [Line Items]
Issuance of common shares, net of issuance costs (in Shares)			1,580
Preferred stock, stated value per unit	$ 1,000			$ 1,000	$ 1,000
Per unit conversion amount, Series A Preferred OP Units (in dollars per unit)	$ 22.50			$ 22.50	$ 22.50
Per unit conversion annual rate, Preferred OP Units	9.00%			9.00%	9.00%
Number of preferred OP Units converted (in shares)					1,392
Units converted from Preferred OP Units (in shares)					185,600
Series A Preferred Stock | Operating Partnership, as General Partner or Managing Member
Class of Stock [Line Items]
Series A Preferred OP Units (in shares)	188			188	188	188
Series C Preferred Stock | Gotham Plaza
Class of Stock [Line Items]
Number of preferred OP Units converted (in shares)				5,000
Units converted from Preferred OP Units (in shares)				17,165
Series C Preferred Stock | Operating Partnership, as General Partner or Managing Member
Class of Stock [Line Items]
Series A Preferred OP Units (in shares)	136,593			136,593	136,593	136,593