Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 59,927	$ 38,720	$ 47,834
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Amount	(22,325)	(22,991)	(23,025)
Income Tax Reconciliation, AFUDC (net)	1,509	(6,095)	(4,462)
Income Tax Reconciliation, Executive Compensation	1,386	2,440	2,596
Income Tax Reconciliation, Treasury Grant	(5,424)	(8,935)	(7,870)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	(13,392)	(3,038)	0
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	2,834	1,563	2,000
Total income tax expense	$ 24,515	$ 1,664	$ 17,073
Effective Income Tax Rate Reconciliation, Percent	8.60%	0.90%	7.50%
Subsidiaries [Member]
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 79,868	$ 63,110	$ 69,735
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Amount	(22,325)	(22,991)	(23,025)
Income Tax Reconciliation, AFUDC (net)	1,509	(6,095)	(4,462)
Income Tax Reconciliation, Executive Compensation	1,386	2,440	2,596
Income Tax Reconciliation, Treasury Grant	(5,424)	(8,935)	(7,870)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	(13,392)	(3,038)	0
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	2,637	1,751	2,174
Total income tax expense	$ 44,259	$ 26,242	$ 39,148
Effective Income Tax Rate Reconciliation, Percent	11.60%	8.70%	11.80%