Property and Equipment Net - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Property, Plant and Equipment
Depreciation and amortization expense	$ 3.9	$ 3.8	$ 7.6	$ 7.6