Debt (Schedule of Lines of Credit Outstanding) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Oct. 11, 2019	Jul. 23, 2019	Dec. 31, 2018	Dec. 15, 2015	Jul. 30, 2015
Line of Credit Facility [Line Items]
Letters of Credit Issued			$ 1,300,000
Document Period End Date	Sep. 30, 2019
Long-term Line of Credit	$ 164,792,000			$ 200,386,000
Debt issuance costs, net of amortization	(1,208,000)			(1,614,000)
Letters of Credit Outstanding, Amount	3,300,000			2,200,000
Line of Credit Facility, Remaining Borrowing Capacity	71,800,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	215,000,000.0				$ 40,000,000.0
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	31,500,000			46,500,000
Line of Credit Facility, Maximum Borrowing Capacity	75,000,000.0					$ 50,000,000.0
Letters of Credit Outstanding, Amount	3,200,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	$ 134,500,000			$ 155,500,000
Subsequent Event [Member]
Line of Credit Facility [Line Items]
Letters of Credit Issued		$ 5,700,000
Line of Credit Facility, Remaining Borrowing Capacity		$ 66,100,000