Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Parent	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income	Non-controlling Interest	Total
Balance at Apr. 30, 2017	$ 383,075	$ 2	$ 162,150	$ 221,050	$ (127)	$ 239
Balance (in shares) at Apr. 30, 2017		23,630,419
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Apr. 30, 2017							$ 383,314
Increase (Decrease) in Stockholders' Equity
Net income (loss)							17,647
Net loss attributable to noncontrolling interest						(216)	216
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	17,863			17,863
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
Balance (in shares) at Apr. 30, 2018		23,908,736
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Apr. 30, 2018							409,056
Increase (Decrease) in Stockholders' Equity
Net income (loss)							47,419
Net loss attributable to noncontrolling interest						(19)	19
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	47,438			47,438
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
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Apr. 30, 2019							462,575
Increase (Decrease) in Stockholders' Equity
Net income (loss)							41,070
Net loss attributable to noncontrolling interest						$ (4)	4
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	41,074			41,074
Unrealized gain on investments	50				50		50
Foreign currency translation	276				276		276
Stock options exercised	100		100				100
Stock options exercised (in shares)		16,189
Restricted stock awards (in shares)		131,991
Restricted stock awards forfeited (in shares)		(12,541)
Tax withholding payment related to net share settlement of equity awards	(1,062)		(1,062)				(1,062)
Tax withholding payment related to net share settlement of equity awards (in shares)		(18,293)
Stock-based compensation	6,227		6,227				6,227
Balance at Apr. 30, 2020	509,901	$ 2	$ 181,481	328,090	$ 328		509,901
Balance (in shares) at Apr. 30, 2020		24,063,639
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Apr. 30, 2020							509,901
Increase (Decrease) in Stockholders' Equity
Adoption of ASU | ASU 2018-09	$ 665			$ 665			$ 665