CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Parent	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interest	Total
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							$ 348,912,000
Balance at Apr. 30, 2015	$ 348,912,000	$ 2,000	$ 148,293,000	$ 201,975,000	$ (1,358,000)
Balance (in shares) at Apr. 30, 2015		23,314,640
Increase (Decrease) in Stockholders' Equity
Net income (loss)							8,966,000
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	8,966,000			8,966,000
Unrealized loss on investments	27,000				27,000		27,000
Reclassifications out of accumulated other comprehensive loss	1,130,000				1,130,000		1,130,000
Stock options exercised	1,122,000		1,122,000				1,122,000
Stock options exercised (in shares)		84,881
Restricted stock awards (in shares)		191,548
Restricted stock awards forfeited (in shares)		(46,753)
Tax withholding payment related to net share settlement of equity awards	(29,000)		(29,000)				(29,000)
Tax withholding payment related to net share settlement of equity awards (in shares)		(1,130)
Reclassification from share-based liability compensation to equity	228,000		228,000				228,000
Tax benefit from stock-based compensation	98,000		98,000				98,000
Purchases of common stock for retirement	(3,756,000)			(3,756,000)			(3,756,000)
Purchases of common stock for retirement (in shares)		(183,261)
Stock-based compensation	4,562,000		4,562,000				4,562,000
Balance at Apr. 30, 2016	361,260,000	$ 2,000	154,274,000	207,185,000	(201,000)
Balance (in shares) at Apr. 30, 2016		23,359,925
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							361,260,000
Net income (loss)							12,457,000
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	12,479,000			12,479,000
Net loss attributable to noncontrolling interest						$ (22,000)	22,000
Unrealized loss on investments	74,000				74,000		74,000
Stock options exercised	3,865,000		3,865,000				3,865,000
Stock options exercised (in shares)		204,130
Restricted stock awards (in shares)		126,557
Restricted stock awards forfeited (in shares)		(60,017)
Tax withholding payment related to net share settlement of equity awards	(5,000)		(5,000)				(5,000)
Tax withholding payment related to net share settlement of equity awards (in shares)		(176)
Reclassification from share-based liability compensation to equity	307,000		307,000				307,000
Tax benefit from stock-based compensation							0
Purchases of common stock for retirement						261,000	261,000
Stock-based compensation	3,709,000		3,709,000				3,709,000
Balance at Apr. 30, 2017	381,954,000	$ 2,000	162,150,000	219,929,000	(127,000)	239,000	381,954,000
Balance (in shares) at Apr. 30, 2017		23,630,419
Increase (Decrease) in Stockholders' Equity
Adoption of ASU 2016-09 | Accounting Standards Update 2016-09	265,000			265,000			265,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							382,193,000
Net income (loss)							19,852,000
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	20,068,000			20,068,000
Net loss attributable to noncontrolling interest						(216,000)	216,000
Unrealized loss on investments	70,000				70,000		70,000
Foreign currency translation	36,000				36,000		36,000
Stock options exercised	2,705,000		2,705,000				2,705,000
Stock options exercised (in shares)		153,211
Restricted stock awards (in shares)		140,787
Restricted stock awards forfeited (in shares)		(6,834)
Tax withholding payment related to net share settlement of equity awards	(397,000)		(397,000)				(397,000)
Tax withholding payment related to net share settlement of equity awards (in shares)		(8,847)
Reclassification from share-based liability compensation to equity	384,000		384,000				384,000
Tax benefit from stock-based compensation							0
Stock-based compensation	5,297,000		5,297,000				5,297,000
Balance at Apr. 30, 2018	$ 410,117,000	$ 2,000	$ 170,139,000	$ 239,997,000	$ (21,000)	$ 23,000	410,117,000
Balance (in shares) at Apr. 30, 2018		23,908,736
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							$ 410,140,000