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Environmental Matters
 3 Months Ended
Mar. 31, 2021
Environmental Remediation Obligations [Abstract]  
Schedule of Environmental Loss Contingencies by Site
The following table summarizes information regarding liabilities related to environmental sites, which are recorded in other current liabilities and other noncurrent liabilities in NW Natural's balance sheet:
Current LiabilitiesNon-Current Liabilities
March 31,December 31,March 31,December 31,
In thousands202120202020202120202020
Portland Harbor site:
Gasco/Siltronic Sediments$7,026 $11,829 $7,596 $42,374 $42,837 $43,725 
Other Portland Harbor2,175 2,554 1,942 6,954 6,574 7,020 
Gasco/Siltronic Upland site13,135 12,822 14,887 39,302 42,833 40,250 
Front Street site1,258 10,704 3,816 1,132 — 1,107 
Oregon Steel Mills— — — 179 179 179 
Total$23,594 $37,909 $28,241 $89,941 $92,423 $92,281 
Environmental Regulatory Table
The following table presents information regarding the total regulatory asset deferred:
March 31,December 31,
In thousands202120202020
Deferred costs and interest (1)
$46,409 $37,586 $44,516 
Accrued site liabilities (2)
113,456 129,977 120,352 
Insurance proceeds and interest(69,492)(80,613)(69,253)
Total regulatory asset deferral(1)
$90,373 $86,950 $95,615 
Current regulatory assets(3)
5,396 4,459 4,992 
Long-term regulatory assets(3)
84,977 82,491 90,623 
(1)     Includes pre-review and post-review deferred costs, amounts currently in amortization, and interest, net of amounts collected from customers.
(2)    Excludes 3.3% of the Front Street site liability as the OPUC only allows recovery of 96.7% of costs for those sites allocable to Oregon, including those that historically served only Oregon customers. Amounts excluded from regulatory assets were $0.1 million at March 31, 2021, $0.4 million at March 31, 2020, and $0.2 million at December 31, 2020,
(3)    Environmental costs relate to specific sites approved for regulatory deferral by the OPUC and WUTC. In Oregon, NW Natural earns a carrying charge on cash amounts paid, whereas amounts accrued but not yet paid do not earn a carrying charge until expended. It also accrues a carrying charge on insurance proceeds for amounts owed to customers. In Washington, neither the cash paid nor insurance proceeds received accrue a carrying charge. Current environmental costs represent remediation costs management expects to collect from customers in the next 12 months. Amounts included in this estimate are still subject to a prudence and earnings test review by the OPUC and do not include the $5.0 million tariff rider. The amounts allocable to Oregon are recoverable through NGD rates, subject to an earnings test.