Note 12 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended					6 Months Ended
	Jan. 31, 2018	Feb. 28, 2019		Nov. 30, 2018	[2]	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018	Aug. 31, 2018
Preferred Stock, Shares Authorized		10,000,000					10,000,000		10,000,000
Preferred Stock, Par or Stated Value Per Share		$ 0.01					$ 0.01		$ 0.01
Preferred Stock, Shares Outstanding, Ending Balance		0					0		0
Common Stock, Shares Authorized		150,000,000					150,000,000		150,000,000
Common Stock, Par or Stated Value Per Share		$ 0.01					$ 0.01		$ 0.01
Common Stock, Shares, Issued, Total		39,690,225					39,690,225		39,264,849
Treasury Stock, Shares, Retired	13,292,689
Treasury Stock, Retired, Cost Method, Amount
Treasury Stock, Shares, Ending Balance		1,590,060					1,590,060		1,072,263
Treasury Stock, Shares, Acquired		214,945				420,000	489,945	584,920
Treasury Stock, Value, Acquired, Cost Method		$ 44,143				$ 81,938	$ 104,584	$ 112,892
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 137,200					$ 137,200
Shares Paid for Tax Withholding for Share Based Compensation							27,852	5,563
Payments Related to Tax Withholding for Share-based Compensation							$ 6,100	$ 1,000
Preferred Stock, Shares Issued, Total		0					0		0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period		23,000	[1]	52,000			75,530	14,839
Treasury Stock [Member]
Treasury Stock, Shares, Retired						13,292,689		13,292,689
Treasury Stock, Retired, Cost Method, Amount	$ (1,700,000)					$ (1,697,206)		$ (1,697,206)
Treasury Stock, Shares, Acquired		214,945				420,000	489,945	585,026
Treasury Stock, Value, Acquired, Cost Method		$ 44,143				$ 81,938	$ 104,584	$ 112,892
Common Stock [Member]
Treasury Stock, Shares, Retired						13,292,689		13,292,689
Treasury Stock, Retired, Cost Method, Amount	100					$ 133		$ 133
Treasury Stock, Shares, Acquired
Treasury Stock, Value, Acquired, Cost Method
Additional Paid-in Capital [Member]
Treasury Stock, Retired, Cost Method, Amount	186,700					186,717		186,717
Treasury Stock, Value, Acquired, Cost Method
Retained Earnings [Member]
Treasury Stock, Retired, Cost Method, Amount	$ 1,500,000					1,510,356		1,510,355
Treasury Stock, Value, Acquired, Cost Method

[1] The majority of the vested restricted stock awards related to the final vesting of awards granted on February 9, 2015, which vested 100% on the four year anniversary date of the grant.

[2] The majority of the vested restricted stock awards related to the final vesting of awards granted on November 1, 2013, which cliff vested 60% after three years on November 1, 2016 and 40% after five years on November 1, 2018.