Retirement Benefit Arrangements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure - Defined contribution plan
Incurred expense for defined contribution arrangements	$ 13,400	$ 15,900	$ 14,500
Zurich Plan
Funded status:
Unfunded pension obligation at beginning of year	41,365	24,614
Change in pension obligation:
Service cost	6,945	6,188
Interest cost	1,682	2,635
Plan participants’ contributions	2,504	1,838
Actuarial loss	7,550	15,796
Plan amendments	0	2,667
Benefits paid	(1,730)	(7,392)
Foreign currency adjustments	(465)	(13,493)
Change in pension obligation	16,486	8,239
Change in fair value of plan assets:
Actual return on plan assets	1,594	1,707
Employer contributions	5,337	5,492
Plan participants’ contributions	2,504	1,838
Benefits paid	(1,730)	(7,392)
Foreign currency adjustments	(259)	(10,157)
Change in fair value of plan assets	7,446	(8,512)
Funded status:
Unfunded pension obligation at end of year	50,405	41,365	$ 24,614
Additional information:
Projected benefit obligation at end of year	151,115	134,629
Accumulated pension obligation at end of year	141,716	127,322
Fair value of plan assets at end of year	$ 100,710	$ 93,264
Pension obligation - assumptions used
Discount rate	1.00%	1.25%	2.25%
Rate of compensation increase	2.25%	2.25%	2.50%
Net periodic benefit cost - assumptions used
Discount rate	1.25%	2.25%	1.75%
Expected return on plan assets	1.25%	2.25%	1.75%
Rate of compensation increase	2.25%	2.50%	2.50%
Defined Benefit Plan Estimated Future Benefit Payments Abstract
2016	$ 4,566
2017	4,531
2018	4,264
2019	4,244
2020	4,454
2021 to 2025	$ 30,061