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Regulatory assets and liabilities | 12 Months Ended
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Dec. 31, 2018
Regulatory Assets and Liabilities Disclosure [Abstract] |
Regulatory assets and liabilities | Regulatory Assets and Liabilities The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:
| Estimated Recovery Period | * | 2018 |  | 2017 |
|  |  | (In thousands)
Regulatory assets: |  |  |  |
Pension and postretirement benefits (a) | (e) |  | $ | 165,898 |  | $ | 163,896 |
Asset retirement obligations (a) | Over plant lives |  | 60,097 |  | 56,078 |
Natural gas costs recoverable through rate adjustments (b) | Up to 1 year |  | 42,652 |  | 14,465 |
Taxes recoverable from customers (a) | Over plant lives |  | 11,946 |  | 12,073 |
Manufactured gas plant sites remediation (a) | - |  | 16,504 |  | 18,213 |
Long-term debt refinancing costs (a) | Up to 19 years |  | 4,898 |  | 5,563 |
Costs related to identifying generation development (a) | Up to 8 years |  | 2,508 |  | 2,960 |
Other (a) (b) | Up to 20 years |  | 35,614 |  | 27,715 |
Total regulatory assets |  |  | 340,117 |  | 300,963 |
Regulatory liabilities: |  |  |  |
Taxes refundable to customers (c) |  |  | 277,833 |  | 279,668 |
Plant removal and decommissioning costs (c) |  |  | 173,143 |  | 176,190 |
Natural gas costs refundable through rate adjustments (d) |  |  | 29,995 |  | 28,514 |
Pension and postretirement benefits (c) |  |  | 15,264 |  | 16,021 |
Other (c) (d) |  |  | 25,197 |  | 18,905 |
Total regulatory liabilities |  |  | 521,432 |  | 519,298 |
Net regulatory position |  |  | $ | (181,315 | ) | $ | (218,335 | )
* | Estimated recovery period for regulatory assets currently being recovered in rates charged to customers.
(a) | Included in deferred charges and other assets - other on the Consolidated Balance Sheets.
(b) | Included in prepayments and other current assets on the Consolidated Balance Sheets.
(c) | Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets.
(d) | Included in other accrued liabilities on the Consolidated Balance Sheets.
(e) | Recovered as expense is incurred or cash contributions are made.
The regulatory assets are expected to be recovered in rates charged to customers. A portion of the Company's regulatory assets are not earning a return; however, these regulatory assets are expected to be recovered from customers in future rates. As of December 31, 2018 and 2017, approximately $313.5 million and $269.1 million, respectively, of regulatory assets were not earning a rate of return. In the fourth quarter of 2017, the Company performed a one-time revaluation of the Company's regulated deferred tax assets and liabilities for the reduction of the corporate tax rate from 35 percent to 21 percent effective January 1, 2018, as identified in the TCJA. In the fourth quarter of 2017, the revaluation of the deferred tax assets and liabilities resulted in a decrease of $15.5 million in taxes recoverable from customers and an increase of $270.0 million in taxes refundable to customers. The revaluation of the Company's regulatory deferred tax assets and liabilities were deferred as the Company worked with the various regulators to plan for amounts expected to be returned to customers. All amounts related to the TCJA are reserved or passed back to customers. The Company has tax settlements in place in most jurisdictions, with new rates in place in 2018 or expected to be in place in the first half of 2019. TCJA filings are pending in Wyoming and Oregon. For more information on the various rate cases, see Note 18. There were no significant changes between the preliminary estimate and final determination of taxes refundable to or recoverable from customers. These regulatory amounts will largely be refunded over the remaining life of the related assets. If, for any reason, the Company's regulated businesses cease to meet the criteria for application of regulatory accounting for all or part of their operations, the regulatory assets and liabilities relating to those portions ceasing to meet such criteria would be removed from the balance sheet and included in the statement of income or accumulated other comprehensive income (loss) in the period in which the discontinuance of regulatory accounting occurs.

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- Definition The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. + References No definition available. + Details
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