Employee Benefit Plans and Shareholder Rights Plan - Narrative (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares $ / units	Dec. 31, 2016 USD ($) $ / shares $ / units	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Other Nonoperating Income (Expense)	$ 6,055	$ 6,244	$ 15,336
Payments Related to Tax Withholding for Share-based Compensation	0
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	(1,702)	(1,921)	(3,198)
US 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost Recognized	17,400	20,000	22,800
Foreign Employee Savings Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost Recognized	9,100	12,100	15,100
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost Recognized		3,200	3,300	$ 3,300
Board of Directors Chairman [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Deferred Compensation Arrangements, Liability, Classified, Noncurrent	3,900	4,500
Trust Value Threshold for Payout to Company	4,000
Norway Member
Defined Benefit Plan Disclosure [Line Items]
Other Nonoperating Income (Expense)		1,100
Foreign Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation		21,000	18,000
Defined Benefit Plan, Fair Value of Plan Assets	22,000	19,000
Employee Severance [Member]
Defined Benefit Plan Disclosure [Line Items]
Postemployment Benefits, Period Expense			23,100
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Plan Cash Award Annual Expense	$ 4,200	$ (4,200)	$ 6,800
Deferred Compensation Plan Cash Award Number of Units	379,892
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	$ 11,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 7 months 28 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	$ 200	$ 150	$ 150
Restricted Stock Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Compensation expense	$ 10,900	$ 13,900	$ 15,900
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards Vesting at end of Vesting Period	80.00%	65.00%	65.00%
Stock Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	$ (3,112)	$ (3,004)	$ (900)