Fair Value Measurements (Narrative) (Details)							3 Months Ended				3 Months Ended
	Dec. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Dec. 31, 2012 GlobalExpense USD ($)	Dec. 31, 2012 GlobalExpense GBP (£)	Jul. 01, 2011 GlobalExpense USD ($)	Jul. 01, 2011 GlobalExpense GBP (£)	Dec. 31, 2012 TripIt USD ($)	Dec. 31, 2011 TripIt	Sep. 30, 2012 TripIt USD ($)	Jan. 24, 2011 TripIt USD ($)	Dec. 31, 2012 Cash equivalents D	Dec. 31, 2012 Short-term investments D Y
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
High range of maturities for financial instruments											90	1
Low range of maturities for financial instruments												90
Contingent consideration arrangement, high range of outcomes					$ 3,200,000	£ 2,000,000	$ 38,300,000		$ 38,300,000	$ 38,300,000
Guaranteed market value of consideration issued, on contingent consideration payment date										82,100,000
Guaranteed market value of consideration issued, per share, on contingent consideration payment date										$ 100.90
Contingent consideration arrangement, low range of outcomes							0		0
Fair value assumption, expected volatility							33.00%	42.00%
Acquisition-related liabilities	4,523,000	4,488,000	3,200,000	2,000,000
Senior convertible notes, carrying value	254,779,000	251,607,000
Senior convertible notes, fair value	$ 402,900,000	$ 438,000,000