Principal Amounts Carrying Amounts and Fair Values of Senior Notes (Detail) (USD $)	Sep. 30, 2014 May 2008 senior notes	Sep. 30, 2013 May 2008 senior notes	May 07, 2008 May 2008 senior notes	Sep. 30, 2014 July 2010 senior notes	Sep. 30, 2013 July 2010 senior notes	Jul. 14, 2010 July 2010 senior notes
Debt Instrument [Line Items]
Principal	$ 202,000,000	$ 210,000,000	$ 275,000,000	$ 245,000,000	$ 245,000,000	$ 245,000,000
Carrying Amounts	202,000,000	210,000,000		245,000,000	245,000,000
Fair Value	$ 214,170,000	$ 221,393,000		$ 248,557,000	$ 241,035,000

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16(a))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

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