Revenue from Contracts with Customers

Accounting Policy

Our revenues are primarily from tariff based sales. We provide gas and/or electricity to customers under these tariffs without a defined contractual term (at-will). As the revenue from these arrangements is equivalent to the electricity or gas supplied and billed in that period (including estimated billings), there will not be a shift in the timing or pattern of revenue recognition for such sales. We have also completed the evaluation of our other revenue streams, including those tied to longer term contractual commitments. These revenue streams have performance obligations that are satisfied at a point in time, and will also not have a shift in the timing or pattern of revenue recognition.

Customers are billed monthly on a cycle basis. To match revenues with associated expenses, we accrue unbilled revenues for electric and natural gas services delivered to customers, but not yet billed at month-end.

Nature of Goods and Services

We currently provide retail electric and natural gas services to three primary customer classes. Our largest customer class consists of residential customers, which include single private dwellings and individual apartments. Our commercial customers consist primarily of main street businesses, and our industrial customers consist primarily of manufacturing and processing businesses that turn raw materials into products.

Electric Segment - Our regulated electric utility business primarily provides generation, transmission, and distribution services to our customers in our Montana and South Dakota jurisdictions. We transfer control and recognize revenue when electricity is delivered to the customer. Payments on our tariff based sales are generally due in 20-30 days after the billing date.

Natural Gas Segment - Our regulated natural gas utility business primarily provides production, storage, transmission and distribution services to our customers in our Montana, South Dakota, and Nebraska jurisdictions. We transfer control and recognize revenue when natural gas is delivered to the customer. Payments on our tariff based sales are generally due in 20-30 days after the billing date.

Disaggregation of Revenue

The following table disaggregates our revenue by major source and customer class (in millions):



	Three Months Ended
	March 31, 2018									March 31, 2017
	Electric			Natural Gas			Total			Electric			Natural Gas			Total

Montana	$	87.2		$	40.9		$	128.1		$	90.8		$	43.8		$	134.6
South Dakota	18.7			11.4			30.1			17.3			10.8			28.1
Nebraska	—			11.4			11.4			—			9.0			9.0
Residential	105.9			63.7			169.6			108.1			63.6			171.7
Montana	83.6			20.6			104.2			88.1			21.9			110.0
South Dakota	24.0			7.9			31.9			22.4			7.4			29.8
Nebraska	—			6.1			6.1			—			4.9			4.9
Commercial	107.6			34.6			142.2			110.5			34.2			144.7
Industrial	10.8			0.5			11.3			10.9			0.5			11.4
Lighting, Governmental, and Irrigation	5.0			0.5			5.5			5.2			0.5			5.7
Total Customer Revenues	229.3			99.3			328.6			234.7			98.8			333.5
Other Tariff and Contract Based Revenues	17.8			10.3			28.1			37.4			11.1			48.5
Total Revenue from Contracts with Customers	247.1			109.6			356.7			272.1			109.9			382.0

Regulatory amortization	(8.8		)	(6.4		)	(15.2		)	(5.9		)	(8.8		)	(14.7		)
Total Revenues	$	238.3		$	103.2		$	341.5		$	266.2		$	101.1		$	367.3