Debt (Schedule of Lines of Credit Outstanding) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 15, 2015	Jul. 30, 2015
Line of Credit Facility [Line Items]
Document Period End Date	Mar. 31, 2020
Long-term Line of Credit	$ 242,758,000	$ 164,642,000
Debt issuance costs, net of amortization	(1,242,000)	(1,358,000)
Letters of Credit Outstanding, Amount	9,000,000.0	9,000,000.0
Line of Credit Facility, Remaining Borrowing Capacity	66,100,000
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	29,000,000	38,000,000
Line of Credit Facility, Maximum Borrowing Capacity	75,000,000.0			$ 50,000,000.0
Letters of Credit Outstanding, Amount	8,900,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	$ 215,000,000	$ 128,000,000