Segment Geographic and Market Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment disclosure
Net sales	$ 233,661	$ 248,044	$ 242,876	$ 217,788	$ 219,387	$ 228,822	$ 218,825	$ 174,003	$ 942,369	$ 841,037	$ 691,864
Operating profit (loss)	20,190	27,053	21,827	18,583	12,323	22,672	23,878	11,168	87,653	70,041	52,877
Assets	842,702				799,093				842,702	799,093	734,260
Depreciation, depletion, and amortization									41,836	36,306	35,906
Capital expenditures									61,029	47,305	60,418
Research and development expenses									9,079	9,231	8,657
Minerals and Materials [Member]
Segment disclosure
Net sales	121,375	123,792	119,851	116,880	114,853	110,332	106,397	97,688	481,898	429,270	336,172
Operating profit (loss)	18,102	20,110	14,699	16,171	11,607	12,341	16,326	14,306	69,082	54,580	34,789
Assets	422,093				402,640				422,093	402,640	384,896
Depreciation, depletion, and amortization									20,082	17,165	16,122
Capital expenditures									27,306	29,700	35,659
Research and development expenses									6,488	5,913	5,344
Environmental [Member]
Segment disclosure
Net sales	52,873	69,543	73,263	50,706	52,356	67,744	63,271	37,227	246,385	220,598	203,231
Operating profit (loss)	592	7,637	7,916	2,296	2,774	8,701	8,148	191	18,441	19,814	25,090
Assets	161,373				160,053				161,373	160,053	151,265
Depreciation, depletion, and amortization									5,389	5,352	6,219
Capital expenditures									8,343	2,557	2,325
Research and development expenses									2,311	2,284	2,339
Oilfield Services [Member]
Segment disclosure
Net sales	53,876	50,175	44,837	44,744	43,569	41,204	39,644	30,204	193,632	154,621	119,821
Operating profit (loss)	5,799	5,787	3,423	4,872	4,758	4,079	4,553	1,228	19,881	14,618	12,753
Assets	194,408				173,239				194,408	173,239	145,981
Depreciation, depletion, and amortization									13,363	11,888	11,767
Capital expenditures									23,097	13,249	11,095
Research and development expenses									238	697	659
Transportation [Member]
Segment disclosure
Net sales	11,782	14,877	14,780	12,674	12,238	14,284	13,583	12,120	54,113	52,225	46,642
Operating profit (loss)	321	770	685	465	466	754	699	511	2,241	24,302	2,163
Assets	3,912				4,071				3,912	4,071	3,552
Depreciation, depletion, and amortization									76	46	38
Capital expenditures									198	92	39
Intersegment Sales/gross profit [Member]
Segment disclosure
Net sales	(6,245)	(10,343)	(9,855)	(7,216)	(3,629)	(4,742)	(4,070)	(3,236)	(33,659)	(15,677)	(14,002)
Corporate [Member]
Segment disclosure
Operating profit (loss)	(4,624)	(7,251)	(4,896)	(5,221)	(7,282)	(3,203)	(5,848)	(5,068)	(21,992)	(21,401)	(21,918)
Assets	60,916				59,090				60,916	59,090	48,566
Depreciation, depletion, and amortization									2,926	1,855	1,760
Capital expenditures									2,085	1,707	11,300
Research and development expenses									$ 42	$ 337	$ 315