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Regulatory Matters (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Regulatory assets
Regulatory assets	$ 802,257	$ 278,258
Less current regulatory assets	(129,951)	(51,676)
Regulatory assets, non-current	672,306	226,582
Regulatory liabilities
Regulatory liabilities	511,390	532,720
Less current regulatory liabilities	(13,580)	(25,061)
Regulatory liabilities, non-current	497,810	507,659
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	426	13,253
Employee benefit plans
Regulatory liabilities
Regulatory liabilities	40,471	40,256
Cost of removal
Regulatory liabilities
Regulatory liabilities	177,003	172,902
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	271,492	285,259
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	21,998	21,050
Deferred energy and gas costs
Regulatory assets
Regulatory assets	68,402	39,035
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	17,066	3,200
Gas price derivatives
Regulatory assets
Regulatory assets	324	2,226
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,469	7,491
Employee benefit plans
Regulatory assets
Regulatory assets	117,886	116,598
Environmental
Regulatory assets
Regulatory assets	1,413	1,413
Loss on reacquired debt
Regulatory assets
Regulatory assets	22,386	22,864
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	51,823	47,515
Decommissioning costs
Regulatory assets
Regulatory assets	7,827	8,988
Gas supply contract termination
Regulatory assets
Regulatory assets	1,013	2,524
Other regulatory assets
Regulatory assets
Regulatory assets	25,806	26,404
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Regulatory assets
Regulatory assets	$ 480,842	$ 0

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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