Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 80,509	$ 86,477	$ 76,907
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization, including amortization of debt issuance costs	38,681	36,374	33,671
Straight-lining of rental income	4,297	2,347	(1,418)
Stock-based compensation expense	394	450	600
Change in operating assets and liabilities:
Tenant and other receivables, net	363	958	(1,801)
Other assets	(2,627)	(9,894)	(4,777)
Amounts due to Vornado	1,626	(1,913)	2,228
Accounts payable and accrued expenses	211	16,049	822
Other liabilities	(28)	(28)	(31)
Net cash provided by operating activities	123,426	130,820	106,201
CASH FLOWS FROM INVESTING ACTIVITIES
Construction in progress and real estate additions	(3,434)	(15,506)	(50,121)
Rego Park II loan participation payment	(200,000)	0	0
Proceeds from maturing short-term investments	0	0	24,998
Principal repayment proceeds from Rego Park II loan participation	1,463	0	0
Net cash used in investing activities	(201,971)	(15,506)	(25,123)
CASH FLOWS FROM FINANCING ACTIVITIES
Debt repayments	(303,707)	(3,440)	(323,193)
Proceeds from borrowing	500,000	0	350,000
Dividends paid	(86,961)	(81,822)	(71,571)
Debt issuance costs	(12,186)	(30)	(4,075)
Net cash provided by (used in) financing activities	97,146	(85,292)	(48,839)
Net increase in cash and cash equivalents and restricted cash	18,601	30,022	32,239
Cash and cash equivalents and restricted cash at beginning of year	374,678	344,656	312,417
Cash and cash equivalents and restricted cash at end of year	393,279	374,678	344,656
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH
Cash and cash equivalents at beginning of year	288,926	259,349	227,815
Restricted cash at beginning of year	85,752	85,307	84,602
Cash and cash equivalents and restricted cash at beginning of year	374,678	344,656	312,417
Cash and cash equivalents at end of year	307,536	288,926	259,349
Restricted cash at end of year	85,743	85,752	85,307
Cash and cash equivalents and restricted cash at end of year	393,279	374,678	344,656
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash payments for interest, excluding capitalized interest of $1,486 in 2015	26,994	19,517	22,354
NON-CASH TRANSACTIONS
Liability for real estate additions, including $21, $54 and $5,795 due to Vornado	705	322	10,139
Write-off of fully amortized and/or depreciated assets	4,265	1,691	20,786
Change in unrealized net gain on available-for-sale securities	$ (2,762)	$ (5,273)	$ (1,455)