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
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
Unrealized (loss) gain on investments	(24)				(24)
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
Increase (Decrease) in Stockholders' Equity
Net income	30,451			30,451
Unrealized (loss) gain on investments	90				90
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
Increase (Decrease) in Stockholders' Equity
Net income	10,426			10,426
Unrealized (loss) gain on investments	(11)				(11)
Stock options exercised	289		289
Stock options exercised (in shares)		208,338
Restricted stock awards (in shares)		163,886
Restricted stock awards forfeited (in shares)		(12,767)
Restricted stock units vested (in shares)		14,926
Tax withholding payment related to net share settlement of equity awards	(77)		(77)
Tax withholding payment related to net share settlement of equity awards (in shares)		(3,971)
Reclassification from share-based liability compensation to equity	401		401
Tax benefit from stock-based compensation	1,490		1,490
Stock-based compensation	3,470		3,470
Balance at Apr. 30, 2013	$ 315,186	$ 2	$ 130,527	$ 185,362	$ (705)
Balance (in shares) at Apr. 30, 2013		22,614,315