Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (EPS) (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended																12 Months Ended
	Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2009		Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Earnings Per Share Disclosure [Line Items]
Numerator for basic earnings per share: income from continuing operations																	$ 71,562	$ 64,457	$ 65,465
Numerator for diluted earnings per share from continuing operations																	$ 71,562	$ 64,457	$ 65,465
Denominator - shares:
Basic weighted-average shares	38,088		39,451		40,010		39,923		41,141		44,446		46,447		47,606		39,359	44,903	48,658
Effect of dilutive securities																	629	405	118
Diluted weighted-average shares	38,687		40,241		40,618		40,439		41,590		44,885		46,870		47,915		39,988	45,308	48,776
Earnings per share:
Basic	$ 0.65	[1]	$ 0.59	[1]	$ 0.19	[1]	$ 0.40	[1]	$ 0.39	[1]	$ 0.40	[1]	$ 0.28	[1]	$ 0.37	[1]	$ 1.82	$ 1.44	$ 1.34
Diluted	$ 0.64	[1]	$ 0.58	[1]	$ 0.19	[1]	$ 0.40	[1]	$ 0.38	[1]	$ 0.40	[1]	$ 0.28	[1]	$ 0.37	[1]	$ 1.79	$ 1.42	$ 1.33

[1] Earnings per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share amounts may not equal the totals for the respective years.