Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	$ 989,470	$ 1,003,860
Defined contribution plan, cost recognized	11,400	9,500	$ 7,900
Salary and Wage, Excluding Cost of Good and Service Sold [Abstract]
Allocated share-based compensation expense	5,900	4,000	5,900
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4,100	9,100	$ 9,600
Pension settlement charges		3,700
Pension - unamortized liability
Defined Benefit Plan Disclosure [Line Items]
Regulatory liability, deferred for future rate treatment	34,500	38,900
Regulatory Liability, Amortization Period			5 years
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit (income) expense	(4,700)	(4,500)	$ (4,100)
Regulatory liabilities	$ 50,500	$ 60,900
Regulatory Liability, Amortization Period	5 years