Operations by Industry Segment and Geographic Area (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Segment	Dec. 31, 2013	Dec. 31, 2012
Operations by Industry Segment and Geographic Area [Abstract]
Number of reportable segments	3
Sales [Abstract]
Total consolidated sales	$ 975,595	$ 932,998	$ 936,273
Interest expense	720	423	339
Depreciation and amortization	24,376	22,265	20,935
Income taxes	19,400	19,028	19,487
Profit (loss)	37,423	39,483	34,729
Assets	1,583,507	1,469,345	1,420,562
Capital expenditures	24,832	27,673	26,018
Net income attributable to controlling interest [Abstract]
Net (income) loss attributable to non-controlling interest	252	(172)	(161)
Income from discontinued operations, net of tax	0	0	3,401
Gain on sale of subsidiary, net of tax	0	0	3,378
Total consolidated net income attributable to controlling interest	34,458	39,042	40,828
Assets [Abstract]
Total assets	805,465	749,291	728,783
Interest expense [Abstract]
Total consolidated interest expense	720	423	339
Depreciation and amortization [Abstract]
Depreciation from discontinued operations	0	0	2,113
Total consolidated depreciation and amortization	24,376	22,265	23,048
Elimination of Intercompany Profit in Inventory [Member]
Assets [Abstract]
Total assets	(7,896)	(4,679)	(4,410)
Elimination of Intercompany Receivables [Member]
Assets [Abstract]
Total assets	(515,625)	(482,768)	(469,254)
Elimination of Investment in Subsidiaries [Member]
Assets [Abstract]
Total assets	(227,051)	(195,199)	(186,556)
Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units	5
Energy Group [Member]
Segment Reporting Information [Line Items]
Number of business units	5
Corporate Group [Member]
Sales [Abstract]
Interest expense	215	394	164
Assets [Abstract]
Total assets	305,282	315,560	321,753
Interest expense [Abstract]
Total consolidated interest expense	215	394	164
Aggregate and Mining Group [Member]
Segment Reporting Information [Line Items]
Number of business units	8
All Others [Member]
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	(35,270)	(30,367)	(33,023)
Depreciation and amortization [Abstract]
Total consolidated depreciation and amortization	853	828	780
Capital expenditures [Abstract]
Total consolidated capital expenditures	413	300	164
Reportable Segments [Member]
Sales [Abstract]
Interest expense	505	29	175
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	72,693	69,850	67,752
Assets [Abstract]
Total assets	1,278,225	1,153,785	1,098,809
Interest expense [Abstract]
Total consolidated interest expense	505	29	175
Depreciation and amortization [Abstract]
Total consolidated depreciation and amortization	23,523	21,437	20,155
Capital expenditures [Abstract]
Total consolidated capital expenditures	24,419	27,373	25,854
Reportable Segments [Member] | Infrastructure Group [Member]
Sales [Abstract]
Total consolidated sales	386,356	398,399	390,753
Interest expense	31	13	143
Depreciation and amortization	7,045	7,417	7,454
Income taxes	1,365	1,567	718
Profit (loss)	29,477	32,814	26,916
Assets	539,794	502,831	478,621
Capital expenditures	5,375	6,214	6,874
Interest expense [Abstract]
Total consolidated interest expense	31	13	143
Reportable Segments [Member] | Energy Group [Member]
Sales [Abstract]
Total consolidated sales	204,356	184,085	190,092
Interest expense	11	4	0
Depreciation and amortization	6,358	6,114	5,320
Income taxes	348	46	175
Profit (loss)	10,316	4,005	6,149
Assets	244,003	223,389	220,356
Capital expenditures	2,875	5,510	9,604
Interest expense [Abstract]
Total consolidated interest expense	11	4	0
Reportable Segments [Member] | Corporate Group [Member]
Sales [Abstract]
Total consolidated sales	0	0	0
Interest expense	215	394	164
Depreciation and amortization	853	828	780
Income taxes	16,452	14,773	17,012
Profit (loss)	(35,270)	(30,367)	(33,023)
Assets	305,282	315,560	321,753
Capital expenditures	413	300	164
Interest expense [Abstract]
Total consolidated interest expense	215	394	164
Reportable Segments [Member] | Aggregate and Mining Group [Member]
Sales [Abstract]
Total consolidated sales	384,883	350,514	355,428
Interest expense	463	12	32
Depreciation and amortization	10,120	7,906	7,381
Income taxes	1,235	2,642	1,582
Profit (loss)	32,900	33,031	34,687
Assets	494,428	427,565	399,832
Capital expenditures	16,169	15,649	9,376
Interest expense [Abstract]
Total consolidated interest expense	463	12	32
Intersegment Eliminations [Member]
Sales [Abstract]
Total consolidated sales	77,218	79,974	74,803
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	(3,217)	(269)	(519)
Assets [Abstract]
Total assets	(27,470)	(37,408)	(31,559)
Intersegment Eliminations [Member] | Infrastructure Group [Member]
Sales [Abstract]
Total consolidated sales	26,661	21,682	29,651
Intersegment Eliminations [Member] | Energy Group [Member]
Sales [Abstract]
Total consolidated sales	17,548	12,857	19,376
Intersegment Eliminations [Member] | Corporate Group [Member]
Sales [Abstract]
Total consolidated sales	0	0	0
Intersegment Eliminations [Member] | Aggregate and Mining Group [Member]
Sales [Abstract]
Total consolidated sales	$ 33,009	$ 45,435	$ 25,776
Design Engineer Manufacture Market [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units	3
Company-owned Dealer [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units	2