Business Segments - Reconciliation of Revenue from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information
Net Sales	$ 115,576	$ 118,365	$ 141,563	$ 121,907	$ 141,331	$ 144,848	$ 190,701	$ 139,548	$ 497,411	$ 616,428	$ 581,064
Segment Assets	370,395				405,171				370,395	405,171	383,249
Depreciation/Amortization									13,579	14,389	15,032
Expenditures for Long-Lived Assets									9,179	6,026	3,658
Rail Technologies and Services
Segment Reporting Information
Net Sales									276,447	321,808	319,524
Infrastructure Solutions
Segment Reporting Information
Net Sales									220,964	294,620	261,540
Operating Segments
Segment Reporting Information
Net Sales									497,411	616,428	581,064
Segment Profit									24,571	43,256	41,055
Segment Assets	299,004				317,011				299,004	317,011	326,916
Depreciation/Amortization									12,222	13,061	13,767
Expenditures for Long-Lived Assets									8,504	5,674	3,356
Operating Segments | Rail Technologies and Services
Segment Reporting Information
Net Sales									276,447	321,808	319,524
Segment Profit									16,321	19,641	19,468
Segment Assets	161,485				186,323				161,485	186,323	175,704
Depreciation/Amortization									6,138	6,469	6,810
Expenditures for Long-Lived Assets									4,599	2,293	941
Operating Segments | Infrastructure Solutions
Segment Reporting Information
Net Sales									220,964	294,620	261,540
Segment Profit									8,250	23,615	21,587
Segment Assets	$ 137,519				$ 130,688				137,519	130,688	151,212
Depreciation/Amortization									6,084	6,592	6,957
Expenditures for Long-Lived Assets									$ 3,905	$ 3,381	$ 2,415