Geographic Information (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	$ 551,406	$ 554,669	$ 507,170	$ 461,901	$ 421,318	$ 410,736	$ 367,112	$ 366,174	$ 2,075,146	$ 1,565,340	$ 1,229,342
Property, Plant and Equipment, Net	35,784				25,209				35,784	25,209	15,238
United States Segment [Member]
Segment Reporting Information [Line Items]
Revenues									1,776,414	1,304,794	1,074,226
Property, Plant and Equipment, Net	29,001				18,953				29,001	18,953	9,762
International Segment [Member]
Segment Reporting Information [Line Items]
Revenues									298,732	260,546	155,116
Property, Plant and Equipment, Net	$ 6,783				$ 6,256				$ 6,783	$ 6,256	$ 5,476