Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,355	$ 1,501
Unamortized leasing fees to Vornado	$ 34,219	$ 35,152
Preferred stock: par value per share (in usd per share)	$ 1.00	$ 1.00
Preferred stock: authorized shares	3,000,000	3,000,000
Preferred stock: issued shares	0	0
Preferred stock: outstanding shares	0	0
Common stock: par value per share (in usd per share)	$ 1.00	$ 1.00
Common stock: authorized shares	10,000,000	10,000,000
Common stock: issued shares	5,173,450	5,173,450
Common stock: outstanding shares	5,107,290	5,107,290
Treasury stock: shares	66,160	66,160