Acquisition of New Mexico Gas Intermediate - Preliminary Purchase Price Allocation (Parenthetical) (Detail) (NMGI and NMGC [Member], USD $) In Millions, unless otherwise specified	Sep. 02, 2014
NMGI and NMGC [Member]
Business Acquisition [Line Items]
Accounts receivables	$ 18.9
Gross contract value	19.6
Contractual receivables not expected to be collected	$ 0.7

Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

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