Nature of Operations and Summary of Significant Accounting Policies - Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Goodwill [Roll Forward]
Gross Balance, Beginning Balance	$ 353,510
Accumulated impairment losses	(85,509)
Net Balance, Beginning Balance	268,001
Acquisitions	(357)
Currency translation	(6,156)
Total 2018 adjustments	(6,513)
Gross Balance, Ending Balance	346,997
Accumulated impairment losses	(85,509)
Net Balance, Ending Balance	261,488
Operating Segment [Member] | Papermaking Systems [Member]
Goodwill [Roll Forward]
Gross Balance, Beginning Balance	247,014
Accumulated impairment losses	(85,509)
Net Balance, Beginning Balance	161,505
Acquisitions	(282)
Currency translation	(3,280)
Total 2018 adjustments	(3,562)
Gross Balance, Ending Balance	243,452
Accumulated impairment losses	(85,509)
Net Balance, Ending Balance	157,943
Operating Segment [Member] | Wood Processing Systems [Member]
Goodwill [Roll Forward]
Gross Balance, Beginning Balance	106,496
Accumulated impairment losses	0
Net Balance, Beginning Balance	106,496
Acquisitions	(75)
Currency translation	(2,876)
Total 2018 adjustments	(2,951)
Gross Balance, Ending Balance	103,545
Accumulated impairment losses	0
Net Balance, Ending Balance	$ 103,545