Notes Payable - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jan. 31, 2013	Jan. 31, 2013	Jan. 31, 2012	Jul. 31, 2012
Notes Payable [Abstract]
Proceeds from borrowing on notes payable	$ 220,000	$ 220,000	$ 0
Weighted average borrowing rate	1.3226%	1.3226%
Repayment of borrowing on notes payable		112,472	0
Outstanding balance on credit facility	112,340	112,340		0
Remaining borrowing capacity	187,660	187,660
Maximum borrowing capacity	$ 337,660	$ 337,660