Retirement Benefit Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Disclosure - Defined contribution plan
Incurred expense for defined contribution arrangements	$ 16,000,000	$ 14,800,000	$ 13,000,000
[ForeignPensionPlansDefinedBenefitMember]
Funded status:
Unfunded pension obligation at beginning of year	17,144,000	9,117,000
Change in pension obligation:
Service cost	7,141,000	5,683,000
Interest cost	3,308,000	3,020,000
Plan participants' contributions	2,174,000	5,761,000
Actuarial loss	8,470,000	7,268,000
Benefits paid	(248,000)	(7,562,000)
Foreign currency adjustments	(850,000)	9,994,000
Settlements	13,178,000	0
Change in pension obligation	6,817,000	24,164,000
Change in fair value of plan assets:
Actual return on plan assets	3,610,000	3,181,000
Employer contributions	6,627,000	6,025,000
Plan participants' contributions	2,174,000	5,761,000
Benefits paid	(248,000)	(7,562,000)
Foreign currency adjustments	(186,000)	8,732,000
Settlement	13,178,000	0
Change in fair value of plan assets	(1,201,000)	16,137,000
Funded status:
Unfunded pension obligation at end of year	25,162,000	17,144,000	9,117,000
Additional information:
Projected benefit obligation	121,156,000	114,339,000
Accumulated pension obligation	116,904,000	110,240,000
Fair value of plan assets	95,994,000	97,195,000
Defined Benefit Plan Estimated Future Benefit Payments Abstract
2012	4,724,000
2013	4,666,000
2014	4,646,000
2015	5,190,000
2016	5,215,000
2017 to 2021	$ 27,051,000
Pension obligation - assumptions used
Pension obligation - discount rate used	2.50%	2.75%	3.25%
Pension obligation - rate of compensation increase	3.50%	3.50%	3.50%
Net periodic benefit cost - assumptions used
Net period benefit cost - discount rate used	2.75%	3.25%	2.75%
Net periodic benefit cost - expected return on plan assets	3.00%	3.60%	3.00%
Net periodic benefit cost - rate of compensation increase	3.50%	3.50%	3.50%