Current Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	May 31, 2013	Aug. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities	$ 114,317	$ 0
Tax-exempt municipal bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities	71,600
Corporate bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Marketable securities	$ 27,700