Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Aug. 28, 2011	Aug. 29, 2010	Aug. 28, 2011	Aug. 29, 2010	Nov. 30, 2010
Segment Reporting Information [Line Items]
Sales	$ 146,468	$ 134,199	$ 391,013	$ 379,761
Income/(loss) before interest, income taxes and equity in loss of affiliate	2,490	10,662	(1,041)	25,550
Assets	749,192		749,192		781,569
Operating Segments [Member]
Segment Reporting Information [Line Items]
Number of segments			4
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Number of segments			3
Fiberglass-Composite Pipe [Member]
Segment Reporting Information [Line Items]
Sales	71,303	60,128	196,045	179,302
Income/(loss) before interest, income taxes and equity in loss of affiliate	11,777	14,784	35,841	46,614
Assets	312,918		312,918		335,135
Water Transmission [Member]
Segment Reporting Information [Line Items]
Sales	41,409	41,432	105,423	108,532
Income/(loss) before interest, income taxes and equity in loss of affiliate	(3,160)	2,121	(11,136)	491
Assets	191,902		191,902		182,576
Infrastructure Products [Member]
Segment Reporting Information [Line Items]
Number of segments			2
Sales	33,757	32,615	89,550	91,933
Income/(loss) before interest, income taxes and equity in loss of affiliate	4,160	3,436	4,944	7,020
Assets	102,464		102,464		92,729
Corporate and unallocated [Member]
Segment Reporting Information [Line Items]
Income/(loss) before interest, income taxes and equity in loss of affiliate	(10,287)	(9,679)	(30,690)	(28,575)
Assets	292,969		292,969		343,070
Eliminations [Member]
Segment Reporting Information [Line Items]
Sales	(1)	24	(5)	(6)
Assets	$ (151,061)		$ (151,061)		$ (171,941)