Employee Benefit Plans and Shareholder Rights Plan - Narrative (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2017 $ / shares	Mar. 31, 2016 $ / shares	Jun. 30, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / units	Dec. 31, 2017 USD ($) $ / units	Dec. 31, 2016 USD ($) $ / units
Defined Benefit Plan Disclosure [Line Items]
Other Nonoperating Income (Expense)				$ 8,788	$ 6,055	$ 6,244
Payments Related to Tax Withholding for Share-based Compensation			$ 0
US 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost				17,700	17,400	20,000
Foreign Employee Savings Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost				10,800	9,100	12,100
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost				2,800	3,200	3,300
Board of Directors Chairman [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Deferred Compensation Arrangements, Liability, Classified, Noncurrent				3,200	3,900
Trust Value Threshold for Payout to Company				4,000
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Plan Cash Award Annual Expense				$ 3,900	$ 4,200	$ (4,200)
Deferred Compensation Plan Cash Award Number of Units				332,756
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Plan Cash Award Per Unit | $ / units				0	0
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Plan Cash Award Per Unit | $ / units				200		150
Restricted Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			3 years
Restricted Stock [Member] | Board of Directors Chairman [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Restricted Stock Units (RSUs) [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			3 years
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 10,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition				1 year 7 months 6 days
Performance Shares [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Final Value | $ / shares	$ 0	$ 0	$ 0
Performance Shares [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Final Value | $ / shares	$ 150	$ 150	$ 200
Restricted Stock Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Compensation expense				$ 10,000	$ 10,900	$ 13,900
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards Vesting at end of Vesting Period				85.00%	80.00%	65.00%
Stock Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities				$ (2,135)	$ (3,112)	$ (3,004)
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation					21,000
Defined Benefit Plan, Fair Value of Plan Assets					$ 22,000