Segment Information, Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Segment Unit	Jun. 30, 2015 USD ($)
Segment Information [Abstract]
Number of reportable segments | Segment			3
Segment Reporting Information [Line Items]
Net sales	$ 294,394	$ 268,042	$ 573,116	$ 556,791
Gross profit	$ 73,452	$ 62,233	$ 145,408	$ 128,279
Gross profit percent	25.00%	23.20%	25.40%	23.00%
Segment profit (loss)	$ 18,141	$ 11,658	$ 35,819	$ 26,574
Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Unit			5
Number of business units that design, engineer, manufacture and market | Unit			3
Number of business units that operate as Company-owned dealers in foreign countries | Unit			2
Aggregate and Mining Group [Member]
Segment Reporting Information [Line Items]
Number of business units that design, engineer, manufacture and market | Unit			8
Energy Group [Member]
Segment Reporting Information [Line Items]
Number of business units that design, engineer, manufacture and market | Unit			5
Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment profit (loss)	18,334	12,268	$ 35,317	27,570
Reportable Segments [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Net sales	152,476	116,097	305,590	251,143
Gross profit	$ 36,583	$ 27,242	$ 76,420	$ 58,188
Gross profit percent	24.00%	23.50%	25.00%	23.20%
Segment profit (loss)	$ 19,673	$ 11,845	$ 41,536	$ 27,356
Reportable Segments [Member] | Aggregate and Mining Group [Member]
Segment Reporting Information [Line Items]
Net sales	99,085	98,829	191,573	205,241
Gross profit	$ 26,141	$ 24,985	$ 51,289	$ 50,957
Gross profit percent	26.40%	25.30%	26.80%	24.80%
Segment profit (loss)	$ 10,947	$ 10,056	$ 20,485	$ 21,650
Reportable Segments [Member] | Energy Group [Member]
Segment Reporting Information [Line Items]
Net sales	42,833	53,116	75,953	100,407
Gross profit	$ 10,514	$ 9,998	$ 17,596	$ 19,117
Gross profit percent	24.50%	18.80%	23.20%	19.00%
Segment profit (loss)	$ 2,626	$ 701	$ 2,433	$ 864
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	16,600	15,991	28,090	39,256
Segment profit (loss)	(193)	(610)	502	(996)
Intersegment Eliminations [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Net sales	4,511	6,690	7,684	11,794
Intersegment Eliminations [Member] | Aggregate and Mining Group [Member]
Segment Reporting Information [Line Items]
Net sales	5,945	3,935	10,796	14,619
Intersegment Eliminations [Member] | Energy Group [Member]
Segment Reporting Information [Line Items]
Net sales	6,144	5,366	9,610	12,843
Corporate [Member]
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Gross profit	$ 214	$ 8	$ 103	$ 17
Gross profit percent	0.00%	0.00%	0.00%	0.00%
Segment profit (loss)	$ (14,912)	$ (10,334)	$ (29,137)	$ (22,300)