Segments and Foreign Operations - Financial Information for Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 229,742	$ 282,879	$ 289,560	$ 273,443	$ 271,924	$ 289,813	$ 289,310	$ 261,711	$ 1,075,624	$ 1,112,758	$ 999,905
Interest expense									(4,309)	(2,357)	(1,594)
Equity in earnings of affiliates									20,572	24,647	13,153
Income (loss) from continuing operations before income taxes									(19,223)	(43,508)	50,877
Investment in affiliates	78,290				88,297				78,290	88,297	69,152
Water Resources [Member]
Segment Reporting Information [Line Items]
Revenues									278,529	274,556	248,907
Income (loss) from continuing operations before income taxes									4,426	(5,967)	17,377
Inliner [Member]
Segment Reporting Information [Line Items]
Revenues									133,256	132,108	116,566
Income (loss) from continuing operations before income taxes									9,936	(13,236)	9,426
Heavy Civil [Member]
Segment Reporting Information [Line Items]
Revenues									278,131	343,760	353,304
Income (loss) from continuing operations before income taxes									(32,308)	(61,649)	9,637
Geoconstruction [Member]
Segment Reporting Information [Line Items]
Revenues									133,247	89,210	77,969
Equity in earnings of affiliates									3,872	3,345	517
Income (loss) from continuing operations before income taxes									517	12,828	11,708
Investment in affiliates	384				20,011				384	20,011	16,666
Water Infrastructure Group [Member]
Segment Reporting Information [Line Items]
Revenues									823,163	839,634	796,746
Income (loss) from continuing operations before income taxes									(17,429)	(68,024)	48,148
Mineral Exploration [Member]
Segment Reporting Information [Line Items]
Revenues									246,582	268,909	199,946
Equity in earnings of affiliates									16,700	21,302	12,636
Income (loss) from continuing operations before income taxes									45,969	62,259	34,947
Investment in affiliates	77,906				68,286				77,906	68,286	52,486
Other [Member]
Segment Reporting Information [Line Items]
Revenues									5,879	4,215	3,213
Income (loss) from continuing operations before income taxes									(7,445)	(4,520)	(400)
Unallocated corporate expenses [Member]
Segment Reporting Information [Line Items]
Income (loss) from continuing operations before income taxes									$ (36,009)	$ (30,866)	$ (30,224)