Retirement Savings Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Retirement Plans [Line Items]
Employees' contributions at a rate	3.00%
Matching Contribution Percentage	50.00%
Employees' contributions at a rate	2.00%
Matching Contribution Amount	$ 1.5	$ 1.6	$ 1.1
Matching Contribution Percentage	100.00%