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