CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Comprehensive Income
Balance at Apr. 30, 2009	$ 207,427	$ 2	$ 110,102	$ 97,860	$ (537)
Balance (in shares) at Apr. 30, 2009		21,470,481
Increase (Decrease) in Stockholders' Equity
Net income	20,716			20,716		20,716
Other comprehensive income (loss):
Unrealized gain (loss) on investments	(223)				(223)	(223)
Comprehensive income	20,493					20,493
Stock options exercised	836		836
Stock options exercised (in shares)		205,132
Restricted stock awards (in shares)		63,000
Restricted stock awards forfeited (in shares)		(6,200)
Tax benefit from stock-based compensation	3,010		3,010
Stock-based compensation	1,654		1,654
Balance at Apr. 30, 2010	233,420	2	115,602	118,576	(760)
Balance (in shares) at Apr. 30, 2010		21,732,413
Increase (Decrease) in Stockholders' Equity
Net income	25,909			25,909		25,909
Other comprehensive income (loss):
Unrealized gain (loss) on investments	(24)				(24)	(24)
Comprehensive income	25,885					25,885
Stock options exercised	619		619
Stock options exercised (in shares)		120,561
Restricted stock awards (in shares)		98,910
Restricted stock awards forfeited (in shares)		(2,000)
Tax benefit from stock-based compensation	1,238		1,238
Stock-based compensation	2,306		2,306
Balance at Apr. 30, 2011	263,468	2	119,765	144,485	(784)
Balance (in shares) at Apr. 30, 2011	21,949,884	21,949,884
Increase (Decrease) in Stockholders' Equity
Net income	30,451			30,451		30,451
Other comprehensive income (loss):
Unrealized gain (loss) on investments	90				90	90
Comprehensive income	30,541					30,541
Stock options exercised	565		565
Stock options exercised (in shares)		141,536
Restricted stock awards (in shares)		157,400
Restricted stock awards forfeited (in shares)		(4,917)
Tax benefit from stock-based compensation	1,428		1,428
Stock-based compensation	3,196		3,196
Balance at Apr. 30, 2012	$ 299,198	$ 2	$ 124,954	$ 174,936	$ (694)
Balance (in shares) at Apr. 30, 2012	22,243,903	22,243,903