Consolidated Statement of Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2016	May 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			$ 592,735
Comprehensive income (loss)	$ 26,214	$ (16,343)	16,879	$ (60,697)
Cash dividends paid on common stock, $0.615 per share			(18,012)
Cash dividends paid on convertible special stock, $45.00 per share	(1,875)	$ (563)	(5,625)	$ (563)
Issuance of treasury stock			181
Stock options exercised			32
Restricted stock issued, net of forfeitures			0
Redemption of common stock to cover tax withholdings			(1,077)
Tax windfall (shortfall) related to share-based incentive compensation			(301)
Amortization of restricted stock			2,466
Balance as of May 31, 2016	587,278		587,278
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			48,369
Stock options exercised			2
Restricted stock issued, net of forfeitures			183
Redemption of common stock to cover tax withholdings			(48)
Balance as of May 31, 2016	48,506		48,506
Convertible special stock, no par value [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			120,289
Balance as of May 31, 2016	120,289		120,289
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			274,319
Issuance of treasury stock			59
Stock options exercised			30
Restricted stock issued, net of forfeitures			(183)
Redemption of common stock to cover tax withholdings			(1,029)
Tax windfall (shortfall) related to share-based incentive compensation			(301)
Amortization of restricted stock			2,466
Balance as of May 31, 2016	275,361		275,361
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			(383,121)
Issuance of treasury stock			122
Balance as of May 31, 2016	(382,999)		(382,999)
Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			(83,460)
Comprehensive income (loss)			(9,684)
Balance as of May 31, 2016	(93,144)		(93,144)
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			607,690
Comprehensive income (loss)			26,082
Cash dividends paid on common stock, $0.615 per share			(18,012)
Cash dividends paid on convertible special stock, $45.00 per share			(5,625)
Balance as of May 31, 2016	610,135		610,135
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of August 31, 2015			8,649
Comprehensive income (loss)			481
Balance as of May 31, 2016	$ 9,130		$ 9,130