Discontinued Operations - Schedule of Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Feb. 28, 2015	Feb. 28, 2014		Feb. 28, 2015	Feb. 28, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax (benefit) expense	$ 53	$ 284		$ 12,204	$ 740
Gain on sale of business				35,036	0
Net income from discontinued operations	1,247	276		18,530	1,038
Discontinued Operations | Storage Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	0	19,264	[1]	31,379	59,183	[1]
Income (loss) before income taxes	401	560	[1]	(4,302)	1,778	[1]
Income tax (benefit) expense	(304)	284	[1]	(2,098)	740	[1]
Gain on sale of business	899	0	[1]	35,036	0	[1]
Income tax expense on gain	357	0	[1]	14,302	0	[1]
Net income from discontinued operations	$ 1,247	$ 276	[1]	$ 18,530	$ 1,038	[1]

[1] Results for the three and nine months ended February 28, 2014 were previously presented in continuing operations.