Accounts Receivable - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jul. 31, 2014	Jul. 31, 2014	Jan. 31, 2014	Jan. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Length of retention period of amount given to project owners		2 years
Allowance for doubtful accounts	$ 5.5	$ 5.5	$ 5.5
Accounts receivable from the owner of a partially completed construction project				5.5
Provision for accounts receivable loss	0	0
Construction Contracts Retainage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contract payment amounts retained by project owners	$ 32.8	$ 32.8	$ 22.7