CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Parent	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest	Total
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							$ 361,260
Balance at Apr. 30, 2016	$ 361,260	$ 2	$ 154,274	$ 207,185	$ (201)
Balance (in shares) at Apr. 30, 2016		23,359,925
Increase (Decrease) in Stockholders' Equity
Net income							13,078
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	13,100			13,100
Net loss attributable to noncontrolling interest						$ (22)	(22)
Unrealized gain on investments	74				74		74
Stock options exercised	3,865		3,865				3,865
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)		(5)				(5)
Tax withholding payment related to net share settlement of equity awards (in shares)		(176)
Reclassification from share-based liability compensation to equity	307		307				307
Business acquisition						261	261
Stock-based compensation	3,709		3,709				3,709
Balance at Apr. 30, 2017	383,075	$ 2	162,150	221,050	(127)	239
Balance (in shares) at Apr. 30, 2017		23,630,419
Increase (Decrease) in Stockholders' Equity
Adoption of ASU | ASU 2016-09	265			265			265
Adoption of ASU | ASU 2014-09	500			500			500
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							383,314
Net income							17,647
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	17,863			17,863
Net loss attributable to noncontrolling interest						(216)	(216)
Unrealized gain on investments	70				70		70
Foreign currency translation	36				36		36
Stock options exercised	2,705		2,705				2,705
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)		(397)				(397)
Tax withholding payment related to net share settlement of equity awards (in shares)		(8,847)
Reclassification from share-based liability compensation to equity	384		384				384
Stock-based compensation	5,297		5,297				5,297
Balance at Apr. 30, 2018	409,033	$ 2	170,139	238,913	(21)	23	409,033
Balance (in shares) at Apr. 30, 2018		23,908,736
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							409,056
Net income							47,419
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	47,438			47,438
Net loss attributable to noncontrolling interest						(19)	(19)
Unrealized gain on investments	57				57		57
Foreign currency translation	(34)				(34)		(34)
Stock options exercised	71		71				71
Stock options exercised (in shares)		12,725
Restricted stock awards (in shares)		57,476
Restricted stock awards forfeited (in shares)		(18,023)
Tax withholding payment related to net share settlement of equity awards	(1,094)		(1,094)				(1,094)
Tax withholding payment related to net share settlement of equity awards (in shares)		(14,621)
Stock-based compensation	7,100		7,100				7,100
Balance at Apr. 30, 2019	$ 462,571	$ 2	$ 176,216	$ 286,351	$ 2	$ 4	462,571
Balance (in shares) at Apr. 30, 2019		23,946,293
Increase (Decrease) in Stockholders' Equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest							$ 462,575