Retirement and Other Postretirement Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 year
Retirement and Other Postretirement Benefit Plans
Period for which the discount rate has declined (in years)	3
Multi-Employer Plan
Minimum percentage of the Plan's total contributions contributed by the entity	5.00%
Expected contribution in 2013	$ 1.0
U.S. Retirement Savings Plan
U.S. retirement saving plan
Maximum percentage of employee's annual compensation allowed as contribution to individual 401(k) retirement saving account (as a percent)	75.00%
Employer contribution as a percentage of employee contribution (as a percent)	50.00%
Maximum employer matching contribution as a percentage of employee's annual compensation (as a percent)	3.00%
U.S. Retirement Savings Plan | Minimum
U.S. retirement saving plan
Additional employer contribution as a percentage of eligible income depending on employee's age (as a percent)	2.00%
Maximum employer contribution to individual 401(k) retirement saving account, after additional contribution (as a percent)	5.00%
U.S. Retirement Savings Plan | Maximum
U.S. retirement saving plan
Additional employer contribution as a percentage of eligible income depending on employee's age (as a percent)	4.00%
Maximum employer contribution to individual 401(k) retirement saving account, after additional contribution (as a percent)	7.00%
UK Defined Contribution Pension Plan
U.S. retirement saving plan
Percentage of pensionable salary that eligible employees can elect to contribute under the first option	3.00%
Percentage of pensionable salary that eligible employees can elect to contribute under the second option	5.00%
Percentage of pensionable salary that eligible employees can elect to contribute under the third option	7.00%
Company's contribution under the first option (as a percent)	5.00%
Company's contribution under the second option (as a percent)	9.00%
Company's contribution under the third option (as a percent)	13.00%