Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			3 Months Ended
	Jan. 31, 2010	Apr. 30, 2013	Jan. 31, 2013	Apr. 30, 2013 Maximum [Member]	Apr. 30, 2013 Minimum [Member]	Apr. 30, 2013 Construction contracts retainages [Member]	Jan. 31, 2013 Construction contracts retainages [Member]
Accounts Receivable (Textual) [Abstract]
Contract payment amounts retained by project owners						$ 17.0	$ 20.2
Length of retention period of amount given to project owners				3 years	9 months
Accounts Receivable (Additional Textual) [Abstract]
Allowance for doubtful accounts		5.5	5.5
The amount of the net proceeds remaining from public auction of the partially completed project	$ 5.5