Debt (Schedule of Lines of Credit Outstanding) (Details) - USD ($)			3 Months Ended	9 Months Ended
	Feb. 25, 2021	Aug. 26, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	May 22, 2020	Dec. 15, 2015	Jul. 30, 2015
Line of Credit Facility [Line Items]
Document Period End Date				Sep. 30, 2021
Long-term Line of Credit				$ 122,717,000		$ 106,687,000
Debt issuance costs, net of amortization				(1,283,000)		(1,313,000)
Letters of Credit Outstanding, Amount				3,800,000		9,800,000
Line of Credit Facility, Remaining Borrowing Capacity				33,600,000
Payments of Debt Issuance Costs	$ 600,000	$ 0.1	$ 300,000	894,000	$ 62,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit								$ 265,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit				19,000,000		7,000,000
Line of Credit Facility, Maximum Borrowing Capacity				35,000,000			$ 75	$ 275,000,000	$ 35,000,000
Letters of Credit Outstanding, Amount				1,400,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit				$ 105,000,000		$ 101,000,000