DEBT, CREDIT FACILITY, AND CAPITAL LEASE OBLIGATIONS (Maturities of Long-term Debt Footnotes) (Detail)	Dec. 31, 2017 USD ($)
Schedule Of Maturities Of Long Term Debt [Line Items]
Unamortized debt issuance expense	$ 10,000,000
Debt discount	2,000,000
Tax Exempt Pollution Control Bonds 2010 Coconino A due 2032 Variable Rate \| Secured Debt
Schedule Of Maturities Of Long Term Debt [Line Items]
Debt instrument, face amount	37,000,000
Tax Exempt Local Furnishings Bonds 2013 Apache A due 2032 Variable Rate \| Unsecured Debt
Schedule Of Maturities Of Long Term Debt [Line Items]
Debt instrument, face amount	$ 100,000,000

Amount, after accumulated amortization, of debt discount.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant