Debt (Schedule of Lines of Credit Outstanding) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2020	May 22, 2020	Dec. 31, 2019	Dec. 15, 2015	Jul. 30, 2015
Line of Credit Facility [Line Items]
Document Period End Date	Sep. 30, 2020
Long-term Line of Credit	$ 93,489,000		$ 164,642,000
Debt issuance costs, net of amortization	(1,011,000)		(1,358,000)
Letters of Credit Outstanding, Amount	7,200,000
Line of Credit Facility, Remaining Borrowing Capacity	27,800,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit				$ 215,000,000.0
Line of Credit Facility, Maximum Borrowing Capacity	275,000,000.0
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	4,000,000		38,000,000
Line of Credit Facility, Maximum Borrowing Capacity	35,000,000.0	$ 75.0			$ 35,000,000.0
Letters of Credit Outstanding, Amount	7,200,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	$ 90,500,000		$ 128,000,000