Business segment data

3 Months Ended

Mar. 31, 2013

Segment Reporting [Abstract]

Business segment data

Business segment data

The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business units due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's chief executive officer and other management. The vast majority of the Company's operations are located within the United States. The Company also has an investment in a foreign country, which consists of Centennial Resources' equity method investment in ECTE.

The electric segment generates, transmits and distributes electricity in Montana, North Dakota, South Dakota and Wyoming. The natural gas distribution segment distributes natural gas in those states as well as in Idaho, Minnesota, Oregon and Washington. These operations also supply related value-added services.

The pipeline and energy services segment provides natural gas transportation, underground storage, processing and gathering services, as well as oil gathering, through regulated and nonregulated pipeline systems primarily in the Rocky Mountain and northern Great Plains regions of the United States. This segment is constructing a diesel topping plant to refine crude oil and also provides cathodic protection and other energy-related services.

The exploration and production segment is engaged in oil and natural gas acquisition, exploration, development and production activities in the Rocky Mountain and Mid-Continent regions of the United States and in and around the Gulf of Mexico.

The construction materials and contracting segment mines aggregates and markets crushed stone, sand, gravel and related construction materials, including ready-mixed concrete, cement, asphalt, liquid asphalt and other value-added products. It also performs integrated contracting services. This segment operates in the central, southern and western United States and Alaska and Hawaii.

The construction services segment specializes in constructing and maintaining electric and communication lines, gas pipelines, fire suppression systems, and external lighting and traffic signalization equipment. This segment also provides utility excavation services and inside electrical wiring, cabling and mechanical services, sells and distributes electrical materials, and manufactures and distributes specialty equipment.

The Other category includes the activities of Centennial Capital, which insures various types of risks as a captive insurer for certain of the Company's subsidiaries. The function of the captive insurer is to fund the deductible layers of the insured companies' general liability and automobile liability coverages. Centennial Capital also owns certain real and personal property. The Other category also includes Centennial Resources' equity method investment in ECTE.

The information below follows the same accounting policies as described in Note 1 of the Company's Notes to Consolidated Financial Statements in the 2012 Annual Report. Information on the Company's businesses was as follows:

Three Months Ended March 31, 2013	External Operating Revenues		Inter- segment Operating Revenues			Earnings on Common Stock
	(In thousands)
Electric	$	64,654	$	—		$	9,825
Natural gas distribution	331,754		—			32,518
Pipeline and energy services	27,716		18,718			2,330
	424,124		18,718			44,673
Exploration and production	115,363		9,812			20,284
Construction materials and contracting	161,977		4,294			(20,582		)
Construction services	229,806		1,574			11,664
Other	334		1,818			305
	507,480		17,498			11,671
Intersegment eliminations	—		(36,216		)	—
Total	$	931,604	$	—		$	56,344

Three Months Ended March 31, 2012	External Operating Revenues		Inter- segment Operating Revenues			Earnings on Common Stock
	(In thousands)
Electric	$	57,963	$	—		$	7,559
Natural gas distribution	307,891		—			25,508
Pipeline and energy services	29,227		20,409			2,760
	395,081		20,409			35,827
Exploration and production	88,494		11,328			12,930
Construction materials and contracting	149,268		151			(24,932		)
Construction services	218,151		25			11,403
Other	1,813		327			391
	457,726		11,831			(208		)
Intersegment eliminations	—		(32,240		)	—
Total	$	852,807	$	—		$	35,619

Earnings from electric, natural gas distribution and pipeline and energy services are substantially all from regulated operations. Earnings from exploration and production, construction materials and contracting, construction services and other are all from nonregulated operations.