Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning Balance at Sep. 30, 2016	$ 269,936	$ 190	$ 242,081	$ 19	$ 27,646
Beginning Balance, Shares at Sep. 30, 2016		19,036
Exercise of stock options	1,079	$ 1	1,078
Exercise of stock options, Shares		72
Vesting of restricted stock units, net of withholding	(202)		(202)
Vesting of restricted stock units, net of withholding, Shares		12
Stock-based compensation expense	13,071		13,071
Income tax benefit from stock option exercises	213		213
Other comprehensive loss, net of tax	(131)			(131)
Net income	17,710				17,710
Ending Balance at Sep. 30, 2017	301,676	$ 191	256,241	(112)	45,356
Ending Balance, Shares at Sep. 30, 2017		19,120
Exercise of stock options and warrants	6,244	$ 2	6,242
Exercise of stock options and warrants, Shares		230
Vesting of restricted stock units, net of withholding	(1,756)	$ 1	(1,757)
Vesting of restricted stock units, net of withholding, Shares		45
Stock-based compensation expense	15,845		15,845
Other comprehensive loss, net of tax	(286)			(286)
Net income	71,956				71,956
Ending Balance at Sep. 30, 2018	$ 393,679	$ 194	276,526	(398)	117,357
Ending Balance, Shares at Sep. 30, 2018		19,395
Cumulative effect adjustment for adoption of new accounting guidance (Note 2)			(45)		45
Exercise of stock options, Shares	231
Exercise of stock options and warrants	$ 6,848	$ 2	6,846
Exercise of stock options and warrants, Shares		231
Vesting of restricted stock units, net of withholding	(4,188)	$ 1	(4,189)
Vesting of restricted stock units, net of withholding, Shares		77
Stock-based compensation expense	19,226		19,226
Other comprehensive loss, net of tax	544			544
Net income	46,383				46,383
Ending Balance at Sep. 30, 2019	$ 462,492	$ 197	$ 298,409	$ 146	$ 163,740
Ending Balance, Shares at Sep. 30, 2019		19,703