Defined Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Defined benefit plans disclosure
Number of defined benefit pension plans	3		3
United Kingdom Defined Benefit Pension Plans
Defined benefit plans disclosure
Number of defined benefit pension plans	2		2
Sponsored defined benefit pension plans, number of subsidiaries	2		2
Components of Net Periodic Benefit Cost:
Service cost	$ 1,120	$ 891	$ 2,248	$ 1,776
Interest cost	2,094	1,866	4,202	3,720
Expected return on plan assets	(2,638)	(2,175)	(5,294)	(4,335)
Amortization of net actuarial loss	336	302	674	602
Participant contributions	(515)	(501)	(1,034)	(999)
Net periodic benefit cost	397	383	796	764
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	5.20%	5.75%	5.20%	5.75%
Expected rate of return on assets (as a percent)	6.50%	6.75%	6.50%	6.75%
Salary increases (as a percent)	4.50%	4.50%	4.50%	4.50%
German Defined Benefit Pension Plan
Defined benefit plans disclosure
Number of defined benefit pension plans	1		1
Sponsored defined benefit pension plans, number of subsidiaries	1		1
Components of Net Periodic Benefit Cost:
Service cost	212	166	424	345
Interest cost	165	144	330	300
Amortization of net actuarial loss	30	17	60	36
Net periodic benefit cost	407	327	814	681
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.60%	5.50%	4.60%	5.50%
Salary increases (as a percent)	2.50%	3.00%	2.50%	3.00%
Supplemental Executive Retirement Plan
Components of Net Periodic Benefit Cost:
Service cost	321	348	641	695
Interest cost	174	173	347	347
Amortization of prior service cost (credit)	(30)	(30)	(59)	(59)
Amortization of net actuarial loss	74	38	147	77
Net periodic benefit cost	539	529	1,076	1,060
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.40%	5.25%	4.40%	5.25%
Salary increases (as a percent)	3.75%	4.00%	3.75%	4.00%
Post-Employment Retiree Health and Welfare Plan
Components of Net Periodic Benefit Cost:
Service cost	30	24	59	48
Interest cost	72	78	145	155
Amortization of net actuarial loss	8		15
Net periodic benefit cost	$ 110	$ 102	$ 219	$ 203
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.70%	5.25%	4.70%	5.25%
Health care cost trend rate (as a percent)	8.50%	7.50%	8.50%	7.50%
Health care cost ultimate trend rate (as a percent)	5.00%		5.00%