Restructuring Costs - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015
Restructuring Cost And Reserve [Line Items]
Restructuring costs	$ 1,005	$ 4,361	$ 1,460	$ 4,551
Water Resources Business Performance Initiative [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs	600		600
Remaining amounts to be incurred	1,500		1,500
FY2016 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs	400		900
Remaining amounts to be incurred	$ 100		100
Total costs incurred			17,100
FY2016 Restructuring Plan [Member] | Operating Segments [Member] | Inliner [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs			100
FY2016 Restructuring Plan [Member] | Operating Segments [Member] | Heavy Civil [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs			400
FY2016 Restructuring Plan [Member] | Operating Segments [Member] | Mineral Services [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs			200
FY2016 Restructuring Plan [Member] | Unallocated Corporate Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs			$ 200