Defined Benefit Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 plan subsidiary	Sep. 30, 2011	Sep. 30, 2012 plan subsidiary	Sep. 30, 2011	Dec. 31, 2011
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	$ 582,000	$ 1,083,000	$ 1,745,000	$ 3,331,000
Interest cost	1,925,000	2,023,000	5,775,000	6,225,000
Expected return on plan assets	(2,569,000)	(2,549,000)	(7,707,000)	(7,843,000)
Amortization of net actuarial loss	293,000	325,000	879,000	999,000
Expected participant contributions		(498,000)		(1,532,000)
Net periodic benefit cost	231,000	384,000	692,000	1,180,000
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.60%	5.20%	4.60%	5.20%
Expected rate of return on assets (as a percent)	5.90%	6.50%	5.90%	6.50%
Salary increases (as a percent)	4.00%	4.50%	4.00%	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	177,000	201,000	547,000	625,000
Interest cost	165,000	157,000	509,000	487,000
Amortization of net actuarial loss	7,000	28,000	23,000	88,000
Net periodic benefit cost	349,000	386,000	1,079,000	1,200,000
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	5.40%	4.60%	5.40%	4.60%
Salary increases (as a percent)	2.50%	2.50%	2.50%	2.50%
Net increase to the liability	5,400,000
Actuarial loss (gain)	6,100,000
Curtailment gain	700,000
Reduction in discount rate (as a percent)	1.90%
Discount rate (as a percent)	3.50%		3.50%		5.40%
Tax on actuarial loss recognized as a componenet of accumulated other comprehensive income	1,900,000
Tax on curtailment gain recognized as a component of accumulated other comprehensive income	200,000
Supplemental Executive Retirement Plan
Defined benefit plans disclosure
Number of defined benefit pension plans	1		1
Components of Net Periodic Benefit Cost:
Service cost	369,000	320,000	1,108,000	961,000
Interest cost	194,000	174,000	582,000	521,000
Amortization of prior service credit	(30,000)	(30,000)	(89,000)	(89,000)
Amortization of net actuarial loss	68,000	74,000	202,000	221,000
Net periodic benefit cost	601,000	538,000	1,803,000	1,614,000
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.30%	4.40%	4.30%	4.40%
Salary increases (as a percent)	3.75%	3.75%	3.75%	3.75%
Post-Employment Retiree Health and Welfare Plan
Defined benefit plans disclosure
Number of post-employment retiree health and welfare plan	1		1
Components of Net Periodic Benefit Cost:
Service cost	25,000	30,000	73,000	89,000
Interest cost	72,000	72,000	218,000	217,000
Amortization of net actuarial loss	9,000	7,000	28,000	22,000
Net periodic benefit cost	$ 106,000	$ 109,000	$ 319,000	$ 328,000
Assumptions Used to Determine Net Periodic Benefit Cost:
Discount rate (as a percent)	4.60%	4.70%	4.60%	4.70%
Health care cost trend rate (as a percent)	8.00%	8.50%	8.00%	8.50%
Health care cost ultimate trend rate (as a percent)	5.00%