Mortgage Loans Payable and Unsecured Credit Facilities (Schedule of Principal Payments on Mortgage Loan Payable, Capital Lease Obligation, Unsecured Term Loans, and Unsecured Credit Facility) (Details) - USD ($)			12 Months Ended
		Sep. 08, 2017	Dec. 31, 2018
Debt Instrument, Gross
2019			$ 1,027,000
2020			1,067,000
2021			176,109,000
2022			151,153,000
2023			101,199,000
Thereafter			197,815,000
Total			628,370,000
Unamortized Debt Issuance Costs
2019			(767,000)
2020			(767,000)
2021			(648,000)
2022			(499,000)
2023			(274,000)
Thereafter			(581,000)
Unamortized Debt Issuance Costs			(3,536,000)
Debt Instrument, Net
2019			260,000
2020			300,000
2021			175,461,000
2022			150,654,000
2023			100,925,000
Thereafter			197,234,000
Total			624,834,000
Revolving Credit Facility [Member]
Debt Instrument, Gross
2021	[1]		100,000,000
Total			$ 100,000,000
Debt Instrument, Net
Line of credit facility extension allowed period		1 year	1 year
Term Loan [Member]
Debt Instrument, Gross
2021			$ 75,000,000
2022			150,000,000
2023			100,000,000
Thereafter			150,000,000
Total			475,000,000
Mortgage Loans Payable [Member]
Debt Instrument, Gross
2019			995,000
2020			1,034,000
2021			1,074,000
2022			1,116,000
2023			1,160,000
Thereafter			42,295,000
Total			47,674,000
Capital Lease Obligation [Member]
Debt Instrument, Gross
2019			32,000
2020			33,000
2021			35,000
2022			37,000
2023			39,000
Thereafter			5,520,000
Total			$ 5,696,000

[1] The revolving credit facility is subject to a one-year extension at the Company's option.