Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2016
Amount outstanding in letters of credit	$ 65.5
Surety Bonds Outstanding	9.3
Holland Creek Metropolitan District [Member]
Credit-enhanced bonds issued amount	6.3
Amount outstanding in letters of credit	6.4
Red Sky Ranch Metropolitan District [Member]
Other long-term liabilities	$ 2.0	$ 2.0	$ 2.0
Estimated cessation date of capital improvement fee payment obligation	Jul. 31, 2031
Employee Housing Bonds [Member]
Amount outstanding in letters of credit	$ 53.4
Workers' Compensation and General Liability Related to Construction and Development Activities [Member]
Amount outstanding in letters of credit	$ 12.1