Operations by Industry Segment and Geographic Area (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) Segment Businessunit	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operations by Industry Segment and Geographic Area [Abstract]
Number of reportable segments | Segment	3
Sales [Abstract]
Total consolidated sales	$ 983,157	$ 975,595	$ 932,998
Interest expense	1,611	720	423
Depreciation and amortization	24,078	24,376	22,265
Income taxes	20,007	19,400	19,028
Profit (loss)	31,566	37,423	39,483
Assets	1,627,514	1,580,307	1,469,345
Capital expenditures	21,288	24,832	27,673
Net income attributable to controlling interest [Abstract]
Net (income) loss attributable to non-controlling interest	831	252	(172)
Total consolidated net income attributable to controlling interest	32,797	34,458	39,042
Assets [Abstract]
Total assets	777,353	802,265	749,291
Elimination of Intercompany Profit in Inventory [Member]
Assets [Abstract]
Total assets	(7,496)	(7,896)	(4,679)
Elimination of Intercompany Receivables [Member]
Assets [Abstract]
Total assets	(583,834)	(515,625)	(482,768)
Elimination of Investment in Subsidiaries [Member]
Assets [Abstract]
Total assets	$ (223,500)	(227,051)	(195,199)
Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Businessunit	5
Energy Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Businessunit	4
Corporate Group [Member]
Assets [Abstract]
Total assets	$ 306,511	302,082	315,560
Aggregate and Mining Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Businessunit	8
All Others [Member]
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	$ (36,623)	(35,270)	(30,367)
Reportable Segments [Member]
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	68,189	72,693	69,850
Assets [Abstract]
Total assets	1,321,003	1,278,225	1,153,785
Reportable Segments [Member] | Infrastructure Group [Member]
Sales [Abstract]
Total consolidated sales	428,737	386,356	398,399
Interest expense	258	31	13
Depreciation and amortization	6,907	7,045	7,417
Income taxes	1,224	1,365	1,567
Profit (loss)	33,890	29,477	32,814
Assets	567,936	539,794	502,831
Capital expenditures	8,043	5,375	6,214
Reportable Segments [Member] | Energy Group [Member]
Sales [Abstract]
Total consolidated sales	183,607	204,356	184,085
Interest expense	10	11	4
Depreciation and amortization	5,553	6,358	6,114
Income taxes	(129)	348	46
Profit (loss)	3,609	10,316	4,005
Assets	256,978	244,003	223,389
Capital expenditures	4,049	2,875	5,510
Reportable Segments [Member] | Corporate Group [Member]
Sales [Abstract]
Total consolidated sales	0	0	0
Interest expense	338	215	394
Depreciation and amortization	899	853	828
Income taxes	18,148	16,452	14,773
Profit (loss)	(36,623)	(35,270)	(30,367)
Assets	306,511	302,082	315,560
Capital expenditures	389	413	300
Reportable Segments [Member] | Aggregate and Mining Group [Member]
Sales [Abstract]
Total consolidated sales	370,813	384,883	350,514
Interest expense	1,005	463	12
Depreciation and amortization	10,719	10,120	7,906
Income taxes	764	1,235	2,642
Profit (loss)	30,690	32,900	33,031
Assets	496,089	494,428	427,565
Capital expenditures	8,807	16,169	15,649
Intersegment Eliminations [Member]
Sales [Abstract]
Total consolidated sales	67,658	77,218	79,974
Net income attributable to controlling interest [Abstract]
Total profit (other losses)	400	(3,217)	(269)
Assets [Abstract]
Total assets	(35,331)	(27,470)	(37,408)
Intersegment Eliminations [Member] | Infrastructure Group [Member]
Sales [Abstract]
Total consolidated sales	22,947	26,661	21,682
Intersegment Eliminations [Member] | Energy Group [Member]
Sales [Abstract]
Total consolidated sales	16,010	17,548	12,857
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	$ 28,701	$ 33,009	$ 45,435
Design Engineer Manufacture Market [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Businessunit	3
Company-owned Dealer [Member] | Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Number of business units | Businessunit	2