Debt (Narrative) (Details) - USD ($)		3 Months Ended
	Aug. 26, 2020	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2020	Aug. 08, 2026	Aug. 08, 2025	Aug. 08, 2024	Dec. 31, 2021	Feb. 25, 2021	Aug. 08, 2019	Dec. 15, 2015
Debt Instrument [Line Items]
Document Period End Date		Mar. 31, 2022
Debt Instrument, Interest Rate, Stated Percentage									3.25%	4.00%
Proceeds from Issuance of Senior Long-term Debt		$ 0	$ 125,000,000
Payments of Debt Issuance Costs	$ 0.1	86,000	$ 595,000
Costs associated with amendment		$ 2,579,000						$ 2,738,000
Line of Credit Facility, Interest Rate at Period End		3.15%
Line of Credit Facility, Remaining Borrowing Capacity		$ 35,000,000
Senior Notes		335,538,000						335,446,000
Letters of Credit Outstanding, Amount		$ 1,500,000						1,700,000
Unsecured Debt	$ 37,500,000
Proceeds from Issuance of Unsecured Debt				$ 37.4
Unsecured Debt [Member]
Debt Instrument [Line Items]
Borrowings on lines of credit											$ 300,000,000
Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End		2.85%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 35,000,000									$ 325,000,000
Borrowings on lines of credit		$ 0						$ 2,000,000
Forecast [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five					$ 50,000,000	$ 12,500,000	$ 12,500,000