Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Net income	$ 130,692	$ 70,667	$ 169,044	$ 102,430
Other comprehensive income (loss):
Reclassification adjustment for loss on derivative instruments included in net income, tax	6	36	17	72
Reclassification adjustment for loss on derivative instruments included in net income, net of tax	47	111	81	223
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit credit, tax	131	148	165	312
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax	387	461	487	906
other comprehensive (income) loss, reclassification adjustment to aoci, postretirement liabiltiy adjustment from regulatory asset, tax	0	(1,086)	0	(1,086)
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset, net of tax	0	(3,265)	0	(3,265)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	387	(2,804)	487	(2,359)
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(22)	(34)	(4)	(119)
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax	(84)	(128)	(14)	(448)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	3	7	6	15
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax	13	25	26	57
Net unrealized gain (loss) on available-for-sale investments	(71)	(103)	12	(391)
Other comprehensive income	363	(2,796)	580	(2,527)
Comprehensive income attributable to common stockholders	$ 131,055	$ 67,871	$ 169,624	$ 99,903