Savings Plan - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Savings Plan [Line Items]
Savings plan maximum percentage of employees contribution allowable	20.00%
Percentage of employer contributions vested per year	25.00%
Maximum employment period considered for vesting of employers' contribution, in years	4
U.S. Qualified Pension Plan
Savings Plan [Line Items]
Maximum percentage of matching contributions made by the employer	100.00%	100.00%	100.00%
Percentage of employer match on employee contribution	4.00%	4.00%	4.00%
Savings Plan
Savings Plan [Line Items]
Amounts charged to statement of operations	10.6	11.3	7.5