BUSINESS SEGMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended									12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 segment	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
BUSINESS SEGMENTS
Number of reportable segments										3
Segment information
Net sales		$ 52,519	$ 50,149	$ 48,687	$ 50,212	$ 54,262	$ 54,890	$ 54,165	$ 45,574	$ 201,567	$ 208,891	$ 154,739
Depreciation and amortization										11,747	11,199	10,713
Income from operations										17,403	18,219	6,789
Equity in earnings of joint ventures												255
Unallocated amounts:
Corporate expenses										(3,565)	(2,686)	(2,214)
Stock-based compensation	(895)									(4,443)	(3,397)	(3,501)
Other income (expense)										(32)	528	2,316
Interest expense										(832)	(1,945)	(3,046)
Interest income										13	8	74
INCOME BEFORE INCOME TAXES										16,552	16,810	6,388
Segment assets
Assets		235,431				213,426				235,431	213,426	201,393
Assets not allocated to segments
Cash and cash equivalents		8,200				5,276				8,200	5,276	4,572	22,411
Prepaid expenses and other assets		5,687				5,647				5,687	5,647	4,600
Deferred tax assets		2,878				1,954				2,878	1,954	1,305
Capital expenditures										15,647	7,726	3,527
Explosive Metalworking Group
Segment information
Net sales										115,333	126,199	98,570
Depreciation and amortization										5,580	5,833	5,891
Income from operations										17,439	16,058	7,461
Segment assets
Assets		100,227				102,473				100,227	102,473	96,344
Assets not allocated to segments
Capital expenditures										4,747	4,338	2,407
Oilfield Products
Segment information
Net sales										77,404	72,782	45,332
Depreciation and amortization										5,631	4,877	4,351
Income from operations										7,047	6,188	2,426
Equity in earnings of joint ventures												255
Segment assets
Assets		112,319				92,070				112,319	92,070	89,169
Assets not allocated to segments
Capital expenditures										10,386	2,904	832
AMK Welding
Segment information
Net sales										8,830	9,910	10,837
Depreciation and amortization										536	489	471
Income from operations										925	2,056	2,617
Segment assets
Assets		6,120				6,006				6,120	6,006	5,403
Assets not allocated to segments
Capital expenditures										514	484	288
Total reportable segments
Segment information
Income from operations										25,411	24,302	12,504
Equity in earnings of joint ventures												255
Segment assets
Assets		218,666				200,549				218,666	200,549	190,916
Assets not allocated to segments
Capital expenditures										$ 15,647	$ 7,726	$ 3,527