Pension and Other Postretirement Benefits - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net actuarial loss, beginning of year	$ 49,260
Amortization of actuarial loss	(2,597)
Actuarial loss (gain)	3,291
Asset gain	(8,102)
Curtailment gain recognized	0
Settlement gain recognized	8	$ (7,630)	$ (128)
Divestiture	(180)
Currency impact	2,679
Net actuarial loss (gain), end of year	44,359	49,260
Prior service credit, beginning of year	(44)
Amortization of prior service credit	41
Divestiture	(10)
Currency impact	24
Prior service cost, end of year	11	(44)
Other Benefits [Member]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net actuarial loss, beginning of year	1,842
Amortization of actuarial loss	0
Actuarial loss (gain)	(3,370)
Asset gain	0
Curtailment gain recognized	0
Settlement gain recognized	0	0	$ 0
Divestiture	0
Currency impact	(17)
Net actuarial loss (gain), end of year	(1,545)	1,842
Prior service credit, beginning of year	0
Amortization of prior service credit	0
Divestiture	0
Currency impact	0
Prior service cost, end of year	$ 0	$ 0