CONTINGENCIES (Details) $ in Millions			1 Months Ended
	Mar. 04, 2016 USD ($)	Feb. 01, 2016 USD ($) project	May. 31, 2015 USD ($)	Mar. 31, 2008 USD ($)	Apr. 30, 2016 USD ($)	Jan. 31, 2015 USD ($)
Loss Contingencies
Aggregate amount self insurance liability reserved					$ 1.3
PPS Engineers, Inc. claims lawsuit | Pending Litigation
Loss Contingencies
Amount of damages sought by plaintiff		$ 0.7
Number of significant project locations involved in the lawsuit | project		1
Damages sought against bond of the project		$ 1.6
Counter claim amount sought	$ 2.5
GPS
Loss Contingencies
GPS mechanics lien against Nebraska project				$ 23.8
Net proceeds held by the bankruptcy court						$ 5.5
Payment received from proceeds deposited with bankruptcy court			$ 1.6