Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net income	$ 74,929	$ 147,971	$ 243,974	$ 250,401
Other comprehensive income (loss):
Reclassification adjustment for loss on derivative instruments included in net income, tax	0	37	17	109
Reclassification adjustment for loss on derivative instruments included in net income, net of tax	0	111	81	334
Postretirement liability adjustment
Amortization of postretirement liability losses included in net periodic benefit credit, tax	98	148	263	460
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax	(6)	461	481	1,367
other comprehensive (income) loss, reclassification adjustment to aoci, postretirement liabiltiy adjustment from regulatory asset, tax	0	0	0	(1,086)
Other Comprehensive (Income) Loss, Reclassification Adjustment to AOCI, Postretirement Liability Adjustment From Regulatory Asset , Net of Tax	0	0	0	(3,265)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(6)	461	481	(1,898)
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(17)	(88)	(21)	(207)
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax	(66)	(329)	(80)	(777)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	3	12	9	27
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax	10	42	36	99
Net unrealized loss on available-for-sale investments	(56)	(287)	(44)	(678)
Other comprehensive income	(62)	285	518	(2,242)
Comprehensive income attributable to common stockholders	74,867	148,256	$ 244,492	$ 248,159
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Net unrealized gain (loss) on available-for-sale investments:
Other comprehensive income	$ 0	$ 111