Revenues and Percentage of Revenues on Geographical Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Revenues	$ 186,075	$ 160,478	$ 159,521	$ 170,349	$ 160,249	$ 150,679	$ 152,824	$ 155,931	$ 676,423	$ 619,683	$ 605,643
Concentration of risk percentage									100.00%	100.00%	100.00%
United States
Segment Reporting Information [Line Items]
Revenues									410,178	389,676	396,036
United States | Sales Revenue, Services, Net
Segment Reporting Information [Line Items]
Concentration of risk percentage									61.00%	63.00%	65.00%
International
Segment Reporting Information [Line Items]
Revenues									$ 266,245	$ 230,007	$ 209,607
International | Sales Revenue, Services, Net
Segment Reporting Information [Line Items]
Concentration of risk percentage									39.00%	37.00%	35.00%