Our utility segment also includes the utility portion of our Mist underground storage facility and our North Mist gas storage expansion in Oregon and NWN Gas Reserves, which is a wholly-owned subsidiary of Energy Corp. Our gas storage segment includes NWN Gas Storage, which is a wholly-owned subsidiary of NWN Energy, Gill Ranch, which is a wholly-owned subsidiary of NWN Gas Storage, the non-utility portion of Mist, and all third-party asset management services. Other includes NNG Financial, non-utility appliance retail center operations, NWN Water, which is pursuing investments in the water sector itself and through its wholly-owned subsidiary FWC Merger Sub, Inc., NWN Energy's equity investment in TWH, which is pursuing development of a cross-Cascades transmission pipeline project and NWN Holding, which is pursuing the potential holding company reorganization of NW Natural. See Note 4 in the 2017 Form 10-K for further discussion of our segments.

Inter-segment transactions were immaterial for the periods presented. The following table presents summary financial information concerning the reportable segments:



	Three Months Ended March 31,
In thousands	Utility		Gas Storage		Other			Total
2018
Operating revenues	$	257,933	$	5,233	$	1,546		$	264,712
Depreciation and amortization	20,543		442		—			20,985
Income (loss) from operations	64,756		3,036		(444		)	67,348
Net income (loss)	39,883		1,898		(244		)	41,537
Capital expenditures	56,894		537		—			57,431
Total assets at March 31, 2018	2,951,918		58,676		18,745			3,029,339
2017
Operating revenues	$	292,726	$	4,541	$	56		$	297,323
Depreciation and amortization	19,624		1,461		—			21,085
Income from operations	77,127		606		(201		)	77,532
Net income	40,192		61		57			40,310
Capital expenditures	38,854		70		—			38,924
Total assets at March 31, 2017	2,799,638		254,260		16,758			3,070,656
Total assets at December 31, 2017	2,961,326		59,583		18,837			3,039,746

Utility Margin

Utility margin is a financial measure consisting of utility operating revenues, reduced by the associated cost of gas, environmental recovery revenues, and revenue taxes. The cost of gas purchased for utility customers is generally a pass-through cost in the amount of revenues billed to regulated utility customers. Environmental recovery revenues represent collections received from customers through our environmental recovery mechanism in Oregon. These collections are offset by the amortization of environmental liabilities, which is presented as environmental remediation expense in our operating expenses. Revenue taxes are collected from our utility customers and remitted to our taxing authorities. The collections from customers are offset by the expense recognition of the obligation to the taxing authority. By subtracting cost of gas, environmental remediation expense, and revenue taxes from utility operating revenues, utility margin provides a key metric used by our chief operating decision maker in assessing the performance of the utility segment. The gas storage segment and other emphasize growth in operating revenues as opposed to margin because they do not incur a product cost (i.e. cost of gas sold) like the utility and, therefore, use operating revenues and net income to assess performance.

The following table presents additional segment information concerning utility margin:



	Three Months Ended March 31,
In thousands	2018		2017
Utility margin calculation:
Utility operating revenues	$	257,933	$	292,726
Less: Utility cost of gas	108,164		143,611
Environmental remediation expense	4,624		6,954
Revenue taxes⁽¹⁾	12,429		—
Utility margin	$	132,716	$	142,161


⁽¹⁾	The change in presentation of revenue taxes was a result of the adoption of ASU 2014-09 "Revenue From Contracts with Customers" and all related amendments on January 1, 2018. This change had no impact on utility margin results as revenue taxes were previously presented net in utility operating revenue. For additional information, see Note 2.