Stock-Based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,181	$ 2,407	$ 4,924	$ 3,616
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	3,030	2,275	4,625	3,367
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 151	$ 132	$ 299	$ 249

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration