Annual report pursuant to Section 13 and 15(d)

Benefit Plans - Net Periodic Pension Expense Benefit (Details)

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Benefit Plans - Net Periodic Pension Expense Benefit (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Pension Plans      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)      
Estimated amortization of actuarial gain for next fiscal period $ 50,000    
Estimated amortization of prior service credit for next fiscal period 0    
Defined Benefit Pension Plans | U.S.      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)      
Service cost 1,219,000 $ 2,130,000 $ 2,778,000
Interest cost 10,115,000 7,680,000 2,913,000
Expected return on plan assets (12,277,000) (9,293,000) (2,885,000)
Amortization of net gain 0 0 0
Curtailment gain recognized 0 (1,311,000) 0
Settlement (gain) loss recognized (48,000) 152,000 (2,000)
Net periodic expense (benefit) (991,000) (642,000) 2,804,000
Defined Benefit Pension Plans | Foreign      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)      
Service cost 3,686,000 2,106,000 0
Interest cost 3,271,000 2,224,000 0
Expected return on plan assets (3,208,000) (2,038,000) 0
Amortization of net gain (9,000) (10,000) 0
Curtailment gain recognized 0 (517,000) 0
Settlement (gain) loss recognized 0 0 0
Net periodic expense (benefit) 3,740,000 1,765,000 0
Supplemental Retirement Plans      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)      
Interest cost 489,000 328,000 0
Net periodic expense (benefit) 489,000 328,000 0
Estimated amortization of actuarial gain for next fiscal period 0    
Other Postretirement Benefits Plans      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)      
Service cost 21,000 37,000 39,000
Interest cost 174,000 151,000 57,000
Amortization of prior service credit (78,000) 0 0
Amortization of net gain (45,000) (17,000) 0
Net periodic expense (benefit) 72,000 $ 171,000 $ 96,000
Estimated amortization of actuarial gain for next fiscal period 44,000    
Estimated amortization of prior service credit for next fiscal period $ 78,000