Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments And Contingencies [Line Items]
Rental expenses	$ 3.3	$ 2.4	$ 2.5
Income from subleases	0	0.1	0.3
Minimum aggregate rental payments required under operating lease ,2013	3.1
2014	2.7
2015	2.2
2016	2.1
2017	2.2
thereafter	$ 4.0