Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies
Rent expense	$ 12,900,000	$ 14,000,000	$ 14,100,000
Minimum future rental commitments under non-cancelable operating leases
2012	13,879,000
2013	11,269,000
2014	6,312,000
2015	5,799,000
2016	5,808,000
2017 and thereafter	10,448,000
Total	53,515,000
Deferred Compensation Arrangements [Line Items]
Aggregate minimum compensation obligations	7,579,000	16,531,000
Maximum separation payments payable for early termination of employment arrangements without cause	10,300,000
Obligation to purchase market data, maintenance and other services	59,700,000
Minimum
Deferred Compensation Arrangements [Line Items]
Aggregate minimum compensation obligations	$ 10,300,000