Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2009 New York Office Space	Jun. 30, 2009 New York Office Space Tenant	Jun. 30, 2008 New York Office Space
Commitments and Contingencies
Term of lease agreement for New York office space (in years)						5 years
Future minimum annual payments for the first twelve month period						$ 5.3
Future minimum annual payments for subsequent twelve month periods						5.7
Number of tenants to whom property is sub-leased					2
Total minimum annual sublease rentals					3.7
Pre-tax loss on sublease				11.7
Rent expense	10.7	11.4	10.6
Future minimum rental payments
2012	15.7
2013	14.2
2014	8.4
2015	7.8
2016	7.9
Thereafter	73.9
Total	$ 127.9