Consolidated Statement of Stockholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012	Aug. 31, 2012
Comprehensive income (loss)	$ 13,505	$ 16,823	$ 34,897	$ 1,067
Cash dividends paid, $0.195 per share			(11,713)
Purchase of treasury stock			(479)
Issuance of treasury stock			220
Stock options exercised			1,174
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures			0
Redemption of common stock to cover tax withholdings			(397)	(374)
Amortization of restricted stock			2,631
Balance as of February 28, 2013	534,022		534,022		507,689
Common Stock [Member]
Stock options exercised			63
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures			84
Redemption of common stock to cover tax withholdings			(22)
Balance as of February 28, 2013	48,083		48,083		47,958
Additional Paid-in Capital [Member]
Issuance of treasury stock			51
Stock options exercised			1,111
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures			(84)
Redemption of common stock to cover tax withholdings			(375)
Amortization of restricted stock			2,631
Balance as of February 28, 2013	262,587		262,587		259,253
Treasury Stock [Member]
Purchase of treasury stock			(479)
Issuance of treasury stock			169
Balance as of February 28, 2013	(371,409)		(371,409)		(371,099)
Accumulated Other Comprehensive Income (Loss) [Member]
Comprehensive income (loss)			10,803
Balance as of February 28, 2013	4,882		4,882		(5,921)
Retained Earnings [Member]
Comprehensive income (loss)			23,564
Cash dividends paid, $0.195 per share			(11,713)
Balance as of February 28, 2013	583,056		583,056		571,205
Noncontrolling Interest [Member]
Comprehensive income (loss)			530
Balance as of February 28, 2013	$ 6,823		$ 6,823		$ 6,293