Other Employee Benefit Programs Defined Contribution Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Company contributions to defined contribution plans	$ 12,476	$ 11,562	$ 9,785
Foreign Plan [Member] | Canadian Retirement Benefit Plan 2 [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	5.00%
Foreign Plan [Member] | Australian Retirement Benefit Plan [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	9.50%	9.50%	9.50%
Foreign Plan [Member] | U.K. Retirement Benefit Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	150.00%
Maximum [Member] | Domestic Plan [Member] | G&W 401k savings plan [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	4.00%
Maximum [Member] | Foreign Plan [Member] | Canadian Retirement Benefit Plan 1 [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Less than fifteen years of service [Member] | Maximum [Member] | Foreign Plan [Member] | U.K. Retirement Benefit Plan [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	7.50%
Fifteen or more years of service [Member] | Maximum [Member] | Foreign Plan [Member] | U.K. Retirement Benefit Plan [Member]
Employer Matching Contribution, Percent of Employees' Gross Pay	9.00%