Derivative Instruments - Additional Information (Detail) (Foreign Exchange Forward) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended						6 Months Ended
	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 EUR (€)	Jun. 30, 2012 GBP (£)	Jun. 30, 2011 EUR (€)	Jun. 30, 2011 GBP (£)	Jun. 30, 2012 Maximum Day
Derivative [Line Items]
Term of derivative contracts (in days)									90
Notional amount of forward foreign currency sale contracts					€ 27.2	£ 23.0	€ 17.0	£ 12.0
Cash received on sale of derivative contracts			71.4	44.0
Net loss on forward foreign currency contracts as a result of change in fair value	$ 0.2	$ 0.2	$ 0.6