Consolidated Statements Of Stockholders' Equity And Comprehensive Income (USD $) In Thousands, except Share data, unless otherwise specified	Total	Add'l Paid-in Capital [Member]	Accum. Other Comp. Loss [Member]	Retained Earnings [Member]	Common Class A [Member]	Common Class B [Member]
Beginning balance at May. 31, 2009	$ 109,693	$ 89,367	$ (106)	$ 20,156	$ 126	$ 150
Beginning balance, shares (in shares) at May. 31, 2009					12,661,000	14,973,000
Comprehensive income:
Net income	18,446			18,446
Available-for-sale debt securities valuation adjustment, net of income taxes	28		28
Total comprehensive income	18,474
Stock options exercised, shares					268,000
Stock options exercised, value	696	693			3
Common stock surrendered for cashless options exercised, shares					(86,000)
Common stock surrendered for cashless options exercised, value	(534)	(533)			(1)
Excess tax benefit from equity instruments	596	596
Stock received for payment of income taxes on stock-based compensation, shares					(2,000)
Stock received for payment of income taxes on stock-based compensation, value	(10)	(10)			0
Special cash dividends	(29,836)	0		(29,836)
Shares and restricted shares issued, shares					52,000
Shares and restricted shares issued, value	0	(1)			1
Restricted stock forfeited, shares					(13,000)
Restricted stock forfeited, value	0	0			0
Stock-based compensation (Note 14)	863	863
Special dividend stock-based compensation expense	506	506
Ending balance at May. 31, 2010	100,448	91,481	(78)	8,766	129	150
Ending balance, shares (in shares) at May. 31, 2010					12,880,000	14,973,000
Comprehensive income:
Net income	12,642			12,642
Available-for-sale debt securities valuation adjustment, net of income taxes	12		12
Total comprehensive income	12,654
Stock options exercised, shares					754,000
Stock options exercised, value	1,661	1,654			7
Common stock surrendered for cashless options exercised, shares					(186,000)
Common stock surrendered for cashless options exercised, value	(1,502)	(1,500)			(2)
Excess tax benefit from equity instruments	2,268	2,268
Stock received for payment of income taxes on stock-based compensation, shares					(387,000)
Stock received for payment of income taxes on stock-based compensation, value	(3,004)	(3,000)			(4)
Special cash dividends	(20,884)	(7,374)		(13,510)
Shares and restricted shares issued, shares					546,000
Shares and restricted shares issued, value	0	(6)			6
Stock-based compensation (Note 14)	4,116	4,116
Special dividend stock-based compensation expense	703	703
Conversion of Class B shares to Class A shares, shares					(7,487,000)	(7,487,000)
Conversion of Class B shares to Class A shares, value	0	0			75	(75)
Ending balance at May. 31, 2011	96,460	88,342	(66)	7,898	211	75
Ending balance, shares (in shares) at May. 31, 2011					21,094,348	7,486,574
Comprehensive income:
Net income	13,727			13,727
Available-for-sale debt securities valuation adjustment, net of income taxes	(19)		(19)
Total comprehensive income	13,708
Stock options exercised, shares					160,000
Stock options exercised, value	761	760			1
Common stock surrendered for cashless options exercised, shares					(39,000)
Common stock surrendered for cashless options exercised, value	(419)	(419)			0
Excess tax benefit from equity instruments	1,625	1,625
Stock received for payment of income taxes on stock-based compensation, shares					(190,000)
Stock received for payment of income taxes on stock-based compensation, value	(1,867)	(1,865)			(2)
Shares and restricted shares issued, shares					749,000
Shares and restricted shares issued, value	0	(8)			8
Restricted stock forfeited, shares					(4,000)
Restricted stock forfeited, value	0	0			0
Stock-based compensation (Note 14)	2,911	2,911
Ending balance at May. 31, 2012	$ 113,179	$ 91,346	$ (85)	$ 21,625	$ 218	$ 75
Ending balance, shares (in shares) at May. 31, 2012					21,769,910	7,486,574