Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
401 (k) Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions under the plan	$ 2.8	$ 2.5	$ 2.0
Defined Contribution Plans
Defined Benefit Plan Disclosure [Line Items]
Company contributions under the plan	$ 3.2	$ 2.1	$ 1.2