Securities purchased under an agreement to sell (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Reverse repurchase agreements	Mar. 31, 2013 Reverse repurchase agreements	Mar. 31, 2014 Minimum	Mar. 31, 2014 Maximum
Investment Holdings [Line Items]
Reverse repurchase agreements outstanding	$ 36.8	$ 38.1
Securities received as collateral	36.2	37.6
Foreign currency gain (loss)			$ (0.01)	$ 0.50
Maturity term for reverse repurchase agreements					30 days	90 days