Debt (Details) $ in Millions	3 Months Ended	12 Months Ended
	Apr. 30, 2016 USD ($) CreditFacility	Jan. 30, 2016 USD ($) CreditFacility
Line of Credit Facility [Line Items]
Number of unsecured credit facilities | CreditFacility	2	2
Available borrowings under credit facilities	$ 80.0	$ 80.0
Days borrowings incurred against facilities	5 days	36 days
Average borrowings outstanding	$ 10.9	$ 12.9
Maximum borrowings outstanding	$ 11.8	$ 28.4
Average interest rate on outstanding borrowings	2.43%	2.22%
August 2015 Facility [Member]
Line of Credit Facility [Line Items]
Expiration date of renewed facility	Aug. 19, 2016	Aug. 19, 2016
Maximum borrowing capacity under renewed facility	$ 30.0	$ 30.0
Line of Credit Facility, Interest Rate Description	Higher of prime, federal funds plus 0.5% or LIBOR	Higher of prime, federal funds plus 0.5% or LIBOR
Description of variable interest rate basis	federal funds	federal funds
Basis spread on variable interest rate (in hundredths)	0.50%	0.50%
Debt outstanding at period end	$ 0.0	$ 0.0
November 2015 Facility [Member]
Line of Credit Facility [Line Items]
Expiration date of renewed facility	Nov. 18, 2016	Nov. 18, 2016
Maximum borrowing capacity under renewed facility	$ 50.0	$ 50.0
Line of Credit Facility, Interest Rate Description	Prime plus 2%	Prime plus 2%
Description of variable interest rate basis	prime	prime
Basis spread on variable interest rate (in hundredths)	2.00%	2.00%
Debt outstanding at period end	$ 0.0	$ 0.0