Long-Term Debt and Commitments Related to Letters of Credit (Narrative) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	$ 325,000
Revolving credit facility, maximum borrowing capacity	425,000
Unused commitments under credit facility	116,114
Revolving credit facility borrowings	$ 206,262	$ 150,433
Number of principal payments	5
Long-term debt, maturities, repayments of principal in next twelve months	$ 11,244
Long-Term Debt, Maturity, Year One	39,921
Long-term debt, maturities, repayments of principal in year two	19,404
Long-term debt, maturities, repayments of principal in year three	222,977
Long-term debt, maturities, repayments of principal in year four	15,000
Long-term debt, maturities, repayments of principal in year five	$ 15,000
Anniversary when principal payments begin	6
Line of Credit Facility, Remaining Borrowing Capacity	$ 8,729
Minimum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.10%
Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.225%
Maximum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Line of credit [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	1.86%
Swing-line borrowings [Member]
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	$ 30,000
Revolving credit facility borrowings	$ 26,262	25,433
Revolving credit facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest coverage ratio	3.00
Revolving credit facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital	3.00
3.99% Senior unsecured notes [Member]
Debt Instrument [Line Items]
Interest rate	3.99%
Debt Instrument, Face Amount	$ 50,000
Senior unsecured notes	$ 50,000	50,000
4.00% Senior unsecured notes [Member]
Debt Instrument [Line Items]
Interest rate	4.00%
Unsecured debt additional shelf note capacity	$ 25,000
Senior unsecured notes	25,000	25,000
Unsecured debt [Member]
Debt Instrument [Line Items]
Unsecured debt additional shelf note capacity	75,000
Debt Instrument, Face Amount	75,000
Senior unsecured notes	75,000	75,000
Unsecured debt, current borrowing capacity	$ 150,000
Accounts receivable securitization [Member]
Debt Instrument [Line Items]
Interest rate	0.90%
Unused commitment fee threshold percent	0.50
Debt instrument variable rate base rate calculation, default rate	2.00%
Accounts receivable securitization [Member] | Base Rate, Federal Funds [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.50%
Accounts receivable securitization [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.10%
Outstanding borrowings, interest rate adjustment (Decrease)	1.00%
Line of credit [Member]
Debt Instrument [Line Items]
Line of credit facility amount committed	$ 208,886
Line of credit facility amount committed	$ 208,886
Line of credit [Member] | Base Rate, Federal Funds [Member]
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.50%
Line of credit [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	1.50%
Line of credit [Member] | Minimum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	0.875%
Line of credit [Member] | Maximum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Outstanding borrowings interest rate margin adjustment, range	1.50%
Letter of credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	$ 94,695	94,435
Letter of credit [Member] | Revolving credit facility [Member]
Debt Instrument [Line Items]
Letters of credit issued	2,624	2,624
Letter of credit [Member] | Accounts receivable securitization [Member]
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	100,000	100,000
Revolving credit facility, maximum borrowing capacity	150,000
Letters of credit issued	$ 89,689	89,689
Debt instrument, term	1 year
Letter of credit [Member] | Accounts receivable securitization [Member] | Minimum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.35%
Letter of credit [Member] | Accounts receivable securitization [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage	0.45%
Letter of credit [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	$ 2,382	$ 2,122
Letter of credit [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	150,000
Line of credit [Member]
Debt Instrument [Line Items]
Revolving credit facility, current borrowing capacity	11,111
Revolving credit facility borrowings	$ 0