Retirement Benefit Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure - Defined contribution plan
Incurred expense for defined contribution arrangements	$ 15,900,000	$ 14,500,000	$ 15,700,000
Zurich Plan
Funded status:
Unfunded pension obligation at beginning of year	24,614,000	32,262,000
Change in pension obligation:
Service cost	6,188,000	6,934,000
Interest cost	2,635,000	2,314,000
Plan participants’ contributions	1,838,000	1,938,000
Actuarial loss (gain)	15,796,000	(8,408,000)
Plan amendments	2,667,000	0
Benefits paid	(7,392,000)	(216,000)
Foreign currency adjustments	(13,493,000)	2,901,000
Settlements	0	(13,783,000)
Change in pension obligation	8,239,000	(8,320,000)
Change in fair value of plan assets:
Actual return on plan assets	1,707,000	3,119,000
Employer contributions	5,492,000	5,922,000
Plan participants’ contributions	1,838,000	1,938,000
Benefits paid	(7,392,000)	(216,000)
Foreign currency adjustments	(10,157,000)	2,348,000
Settlements	0	(13,783,000)
Change in fair value of plan assets	(8,512,000)	(672,000)
Funded status:
Unfunded pension obligation at end of year	41,365,000	24,614,000	32,262,000
Additional information:
Projected benefit obligation at end of year	134,629,000	126,390,000
Accumulated pension obligation at end of year	127,322,000	123,524,000
Fair value of plan assets at end of year	93,264,000	101,776,000
Pension obligation - assumptions used
Discount rate	1.25%	2.25%	1.75%
Rate of compensation increase	2.25%	2.50%	2.50%
Net periodic benefit cost - assumptions used
Discount rate	2.25%	1.75%	2.50%
Expected return on plan assets	2.25%	1.75%	2.50%
Rate of compensation increase	2.50%	2.50%	3.50%
Defined Benefit Plan Estimated Future Benefit Payments Abstract
2015	3,959,000
2016	4,461,000
2017	4,332,000
2018	4,108,000
2019	4,086,000
2020 to 2024	$ 26,983,000