Business and Significant Accounting Policies (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 sqft	Dec. 31, 2011	Dec. 31, 2010
Number of Reportable Segments	3
Unbilled Receivables, Current	$ 34,000,000	$ 29,200,000
Share-based Compensation	36,378,000	32,865,000	32,634,000
Operating Leases, Rent Expense, Net	30,300,000	26,200,000	23,500,000
Depreciation	25,369,000	25,539,000	25,349,000
Capitalized Computer Software, Net	14,400,000	13,600,000
Capitalized Computer Software, Amortization	7,400,000	7,800,000	7,900,000
Number of Leasable Square Feet (in Square feet)	213,000
Number of Leased Properties	3
Operating Lease Expiration Period	15 years
Deferred Rent Credit	25,000,000
Deferred Rent Credit, Current	21,000,000
Payments for Capital Improvements	44,337,000	41,954,000	21,694,000
Leasehold Improvements, Gross	13,000,000	9,000,000
Amortization of Intangible Assets	4,402,000	6,525,000	10,525,000
Goodwill	519,506,000	508,550,000	510,265,000	[1]
Pension Expense	2,600,000	2,700,000	2,400,000
Debt, Current	205,000,000	200,000,000
Foreign Currency Transaction Gain (Loss), Realized	(2,300,000)	(1,300,000)	(4,800,000)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	3,000	5,300	7,900
Payments for Repurchase of Common Stock	111,304,000	211,986,000	99,820,000
Ideas International Limited [Member]
Amortization of Intangible Assets	8,500,000
Goodwill	7,500,000
Foreign Currency Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	600,000	(1,200,000)	2,800,000
Stamford [Member]
Payments for Capital Improvements	17,000,000	9,500,000
Trade Names [Member]
Amortization of Assets Against Earnings, Period, Minimium	2 years
Amortization of Assets Against Earnings, Period, Maximum	5 years
Customer Relationships [Member]
Amortization of Assets Against Earnings, Period	4 years
Content [Member]
Amortization of Assets Against Earnings, Period	4 years
Computer Software, Intangible Asset [Member]
Amortization of Assets Against Earnings, Period	3 years
Accounts Payable and Accrued Liabilities [Member]
Deferred Rent Credit, Current	1,500,000
Other Liabilities [Member]
Deferred Rent Credit, Current	$ 19,500,000

[1] The Company does not have accumulated goodwill impairment losses.