Earnings per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended
	Aug. 31, 2011	Aug. 31, 2010
Basic EPS:
Income from continuing operations	$ 16,963	$ 14,047
Less income attributable to participating shares	(596)
Income from continuing operations available to common shareholders	16,367	14,047
Loss from discontinued operations	(314)	(373)
Net income attributable to AAR available to common shareholders	16,053	13,674
Basic shares:
Weighted average common shares outstanding (in shares)	38,869,000	38,411,000
Earnings per share - basic:
Earnings from continuing operations (in dollars per share)	$ 0.42	$ 0.37
Loss from discontinued operations, net of tax (in dollars per share)	$ (0.01)	$ (0.01)
Earnings per share - basic (in dollars per share)	$ 0.41	$ 0.36
Diluted EPS:
Income from continuing operations	16,963	14,047
Less income attributable to participating shares	(548)
Add after-tax interest on convertible debt	1,461	1,371
Income from continuing operations available to common shareholders	17,876	15,418
Loss from discontinued operations	(314)	(373)
Net income attributable to AAR available to common shareholders - Diluted	$ 17,562	$ 15,045
Diluted shares:
Weighted average common shares outstanding (in shares)	38,869,000	38,411,000
Additional shares from the assumed exercise of stock options (in shares)	387,000	85,000
Additional shares from the assumed conversion of convertible debt (in shares)	4,090,000	4,068,000
Weighted average common shares outstanding - diluted (in shares)	43,346,000	42,564,000
Earnings per share - diluted:
Earnings from continuing operations (in dollars per share)	$ 0.41	$ 0.36
Loss from discontinued operations, net of tax (in dollars per share)		$ (0.01)
Earnings per share - diluted (in dollars per share)	$ 0.41	$ 0.35
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)	210,000	1,232,000