Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefits Disclosure [Line Items]
Company's matching contribution for 401(k) plan of the first 4% employee contribution	100.00%	100.00%	100.00%
Employees contribution to 401(k) plan that is 100 % matched by employer	4.00%	4.00%	4.00%
401(k) plan expense	$ 4,600,000	$ 1,600,000	$ 1,700,000
401(k) plan expense		2,800,000	2,900,000
Retirement Savings Contributions
Employee Benefits Disclosure [Line Items]
401(k) plan expense	2,500,000
Non Discretionary Matching Contributions
Employee Benefits Disclosure [Line Items]
401(k) plan expense	2,100,000
Maximum
Employee Benefits Disclosure [Line Items]
Discretion of contribution to each eligible employee's 401(k) plan irrespective of the employees' contribution	4.00%
United States
Employee Benefits Disclosure [Line Items]
Percentage of company contribution	7.50%
Defined contribution plan employees vesting percentage beginning at the end of their second year	20.00%
Defined contribution plan additional employees vesting percentage being fully vested	6 years
United States | Maximum
Employee Benefits Disclosure [Line Items]
Bonus to employees		2,500	2,500
United Kingdom
Employee Benefits Disclosure [Line Items]
401(k) plan expense	$ 1,900,000	$ 1,700,000	$ 1,500,000
Fully vested contributions as percentage of employee's gross salary	15.00%