Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Nov. 30, 2012	Nov. 30, 2011
Cash flows from operating activities:
Net income	$ 21,672	$ 17,201
Adjustments to reconcile net income to net cash provided by operating activities:
Earnings from unconsolidated affiliates	(866)	(848)
Depreciation and amortization	9,654	8,335
Amortization of deferred loan costs	111	128
Foreign currency loss	188	164
Deferred income taxes	2,038	2,029
Non-cash compensation cost	2,120	2,620
(Increase) decrease:
Receivables	(18,361)	(5,380)
Inventory	(1,393)	(1,361)
Prepaid expenses and other current assets	1,174	1,594
Increase (decrease):
Accounts payable	182	(6,057)
Other accrued liabilities	5,005	1,704
Income taxes	(1,805)	(770)
Net cash provided by operating activities	19,719	19,359
Cash flows from investing activities:
Capital expenditures	(12,654)	(10,739)
Business acquisitions, net of cash acquired	(18,144)	(2,268)
Proceeds from sale of assets		220
(Increase) decrease in other assets, net	(8)	64
Net cash used in investing activities	(30,806)	(12,723)
Cash flows from financing activities:
Borrowings (payments) under revolving credit agreement, net	19,000	(861)
Payments related to term and auto notes		(179)
Debt issuance costs		(759)
Corporate tax effect from share-based payment arrangements	1,997	609
Issuance of common stock from share-based payment arrangements	3,394	669
Payments related to withholding tax for share-based payment arrangements	(1,517)	(853)
Net cash provided by (used in) financing activities	22,874	(1,374)
Effect of exchange rate changes on cash	221	(592)
Net increase in cash and cash equivalents	12,008	4,670
Cash and cash equivalents at beginning of period	22,477	14,078
Cash and cash equivalents at end of period	$ 34,485	$ 18,748