Debt and Credit Facilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Line of Credit Facility [Line Items]
Debt borrowing capacity	$ 600,000
Borrowings outstanding	426,250	$ 427,500
Line of credit borrowings outstanding	230,000
Stand-by letters of credit	$ 53,900
Wells Fargo Term Loan Mature May 14, 2024
Schedule of Capitalization, Long-Term Debt [Line Items]
Term loan maturity	May 14, 2024
Term loan outstanding amount	$ 100,000
Term loan interest rate	1.05%
BMO Harris Bank N.A. Term Loan Mature May 14, 2024
Schedule of Capitalization, Long-Term Debt [Line Items]
Term loan maturity	May 14, 2024
Term loan face amount	$ 100,000
Term loan outstanding amount	$ 96,300
Term loan interest rate	1.28%
Frequency of periodic payment	quarterly
Periodic payment, principal	$ 1,250
Wells Fargo Bank, N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Debt borrowing capacity	$ 300,000
Committed credit facilities maturity	May 14, 2024
Interest rate swap facility, amount	$ 75,000
Line of credit borrowings outstanding	$ 75,000
Line of credit facility, interest rate	0.99%
Interest rate swap facility, fixed interest	2.32%
Interest rate swap facility, maturity date	May 14, 2024
Maximum limit for aggregate amount of letters of credit issued	$ 75,000
BMO Harris Bank N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Debt borrowing capacity	$ 300,000	$ 200,000
Committed credit facilities maturity	May 14, 2024
Interest rate swap facility, amount	$ 75,000
Line of credit borrowings outstanding	$ 75,000
Line of credit facility, interest rate	0.93%
Interest rate swap facility, fixed interest	2.36%
Interest rate swap facility, maturity date	May 14, 2024
Debt instrument, description of variable rate basis	SOFR
Debt instrument, basis spread on variable rate	0.10%
Additional Outstanding Debt Under Credit Facilities
Line of Credit Facility [Line Items]
Line of credit borrowings outstanding	$ 80,000
Line of credit facility, interest rate	1.02%
SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument, description of variable rate basis	SOFR
Debt instrument, basis spread on variable rate	0.10%
Term SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument description of fixed rate basis	Term SOFR
Debt instrument basis spread on fixed rate one month term	0.10%
Debt instrument basis spread on fixed rate three month term	0.15%
Debt instrument basis spread on fixed rate six month term	0.25%
Minimum | Wells Fargo Bank, N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Letter of credit fee on outstanding amount, percentage	0.55%
Unused capacity commitment fee, percentage	0.11%
Minimum | BMO Harris Bank N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	0.70%
Minimum | SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument, basis spread on variable rate	0.675%
Minimum | Term SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument, basis spread on variable rate	0.675%
Maximum | Wells Fargo Bank, N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Letter of credit fee on outstanding amount, percentage	0.80%
Unused capacity commitment fee, percentage	0.15%
Maximum | BMO Harris Bank N.A. Line of Credit Facility, Mature May 14, 2024
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	1.50%
Maximum | SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument, basis spread on variable rate	0.925%
Maximum | Term SOFR | Wells Fargo Debt Facilities
Schedule of Capitalization, Long-Term Debt [Line Items]
Debt instrument, basis spread on variable rate	0.925%