Face (par) amount of debt instrument at time of issuance.

Reference 1: 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Condensed Consolidating Financial Information - Guarantor Subsidiaries - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Sep. 30, 2017	Mar. 17, 2014
Supplemental Guarantor Financial Information [Line Items]
Ownership of subsidiaries (percent)		100.00%
5.25% Senior Notes due March 15, 2019 [Member] \| Senior Notes [Member]
Supplemental Guarantor Financial Information [Line Items]
Debt issued			$ 500,000,000
Interest rate on Senior Notes	5.25%		5.25%