CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net Income	$ 17,215,000	$ 23,691,000	$ 51,551,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	23,008,000	22,198,000	20,975,000
Amortization of debt premium	(225,000)	(225,000)	(312,000)
Stock-based compensation expense	481,000	427,000	399,000
Gain on property exchange		(8,742,000)
Gain on divestiture of real property			(13,043,000)
Gains on purchase of minority interests in majority-owned LLCs			(25,409,000)
Changes in assets and liabilities:
Rent receivable	(1,204,000)	(290,000)	(555,000)
Accrued expenses and other liabilities	3,000	(184,000)	(509,000)
Tenant reserves, deposits and prepaid rents	1,377,000	1,781,000	(303,000)
Accrued interest	122,000	(41,000)	(62,000)
Leasing costs	(627,000)	(556,000)	(787,000)
Other, net	583,000	119,000	851,000
Net cash provided by operating activities	40,733,000	38,178,000	32,796,000
Cash flows from investing activities:
Investments in LLCs	(5,454,000)	(667,000)	(1,337,000)
Repayments of advances made to LLCs	851,000	306,000
Advances made to LLCs		(22,795,000)
Cash distributions in excess of income from LLCs	1,362,000	224,000	1,029,000
Cash distribution of refinancing proceeds from LLCs		1,045,000	2,280,000
Additions to real estate investments, net	(11,204,000)	(5,257,000)	(2,866,000)
Cash received for property exchange	0	2,000,000	17,300,000
Deposits on real estate assets		(150,000)	(100,000)
Net cash paid for acquisition of properties	(60,389,000)	(16,765,000)	(15,600,000)
Cash paid to acquire minority interests in majority-owned LLCs		(2,250,000)	(4,744,000)
Net cash used in investing activities	(74,834,000)	(44,309,000)	(4,038,000)
Cash flows from financing activities:
Net borrowings on line of credit	59,350,000	52,400,000
Net repayments on line of credit			(3,950,000)
Proceeds from mortgage notes payable		5,200,000
Repayments of mortgage notes payable	3,230,000	17,826,000	12,327,000
Financing costs paid	(307,000)	(1,114,000)
Dividends paid	(35,138,000)	(34,089,000)	(32,718,000)
Partial settlement of dividends equivalent rights	(30,000)	(75,000)	(94,000)
Issuance of shares of beneficial interest, net	13,492,000	1,668,000	19,274,000
Net cash provided by/(used in) financing activities	34,137,000	6,164,000	(29,815,000)
Increase/(decrease) in cash and cash equivalents	36,000	33,000	(1,057,000)
Increase in cash due to recording of LLCs on a consolidated/unconsolidated basis			1,581,000
Cash and cash equivalents, beginning of period	3,894,000	3,861,000	3,337,000
Cash and cash equivalents, end of period	3,930,000	3,894,000	3,861,000
Supplemental disclosures of cash flow information:
Interest paid	8,895,000	8,025,000	8,268,000
Supplemental disclosures of non-cash transactions:
Financing assumed in acquisition	$ 7,499,000
Property Exchange Transaction:
Net assets acquired in property exchange		9,886,000
Net assets relinquished in property exchange		$ (3,144,000)
Consolidation Of Limited Liability Companies
Supplemental disclosures of non-cash transactions:
Net real estate investments			84,064,000
Cash and cash equivalents			1,581,000
Intangible assets			6,490,000
Rent receivable - other			388,000
Deferred charges and other assets, net			100,000
Investment in LLCs			(28,616,000)
Mortgage notes payable, non-recourse to us			(29,758,000)
Accrued interest			(116,000)
Accrued expenses and other liabilities			(1,245,000)
Tenant reserves, escrows, deposits and prepaid rents			(485,000)
Note payable to previous third-party member			(2,250,000)
Gains on purchases of minority interests in majority-owned LLCs			(25,409,000)
Cash paid for purchase of minority interests in majority-owned LLCs			$ 4,744,000