Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 months	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2008
Summary Of Significant Accounting Policies [Line Items]
Revenue recognition period (in months)	39
Unrealized gain (loss) on auction rate securities	$ 7,000	$ (200,000)	$ 1,000,000
Software and website developments costs, net	37,341,000	29,875,000
Amortization expense of software and website development costs	12,300,000	9,700,000	7,600,000
Market capitalization				602,000,000	689,000,000
Book value, including goodwill				502,000,000	430,000,000
Cumulative book income position period (in years)	3
Uncertain tax positions	800,000	1,000,000	800,000			500,000
Accrued interest and penalties related to tax positions	100,000	100,000
Advertising and promoting costs	1,000,000	1,000,000	1,300,000
Income tax benefit related to stock-based compensation expense	$ 4,200,000	$ 4,000,000	$ 6,200,000
Transaction Services Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected customer relationship period	4
Software And Website Development Costs [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life, minimum (in years)	2
Estimated useful life, maximum (in years)	7
Executive Officers [Member]
Summary Of Significant Accounting Policies [Line Items]
Options vested, expiration period (in months)	12
Stock Options [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting period (in years)	four
Options granted, expiration period (in years)	7
Options vested, expiration period (in months)	3
Exchanged options granted, vesting period description	Exchanged options granted under the SOEP will vest 25% after six months from the new grant date, 25% twelve months from the new grant date, and 1/48 from the new options grant date each month thereafter.
Stock Options [Member] | Directors [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting period (in years)	three
Stock Options Granted Prior To July 11, 2007 [Member]
Summary Of Significant Accounting Policies [Line Items]
Options granted, expiration period (in years)	10
Restricted Common Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting period (in years)	four
Restricted Common Stock [Member] | Directors [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting period (in years)	one
L T I P Awards [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting period (in years)	three
Maximum [Member] | Subscription Services Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected customer relationship period	60
Minimum [Member] | Subscription Services Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected customer relationship period	36