The cash outflow for acquisition of or capital improvements on other tangible or intangible assets not otherwise defined in the taxonomy.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Name:	us-gaap_PaymentsToAcquireOtherProductiveAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

UTILITY PLANT AND JOINTLY-OWNED FACILITIES (Springerville Acquisition) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unusual or Infrequent Item [Line Items]
Payments to Acquire Other Productive Assets		$ 85,000	$ 45,753	$ 19,608
Settled Litigation [Member] \| Springerville Unit 1 Third Party Owner Allegation [Member]
Unusual or Infrequent Item [Line Items]
Payments to Acquire Other Productive Assets	$ 85,000
Percentage Of Ownership In Generating Units	100.00%