Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Mar. 31, 2018	$ 689,524	$ 444	$ (67,078)	$ 619,905	$ 140,457	$ (4,204)
Beginning Balance (in shares) at Mar. 31, 2018		44,375,337	1,725,312
Restricted stock units issued		$ 4		(4)
Restricted stock units issued (in shares)		427,431
Stock options exercised	12,949	$ 5		12,944
Stock options exercised (in shares)		485,363
Stock issued under employee stock purchase plan	3,052			3,052
Stock issued under employee stock purchase plan (in shares)		12,467
Stock issued to directors	116			116
Stock issued to directors (in shares)		316
Return of common stock to pay withholding taxes on restricted stock	(71,776)	$ (2)	$ (71,774)
Return of common stock to pay withholding taxes on restricted stock (in shares)		177,929	(177,929)
Stock compensation expense	54,494			54,494
Other comprehensive income (loss)	(10,485)					(10,485)
Net income	259,016				259,016
Ending Balance at Mar. 31, 2019	936,890	$ 451	$ (138,852)	690,507	399,473	(14,689)
Ending Balance (in shares) at Mar. 31, 2019		45,122,985	1,903,241
Restricted stock units issued		$ 4		(4)
Restricted stock units issued (in shares)		392,872
Stock options exercised	3,748	$ 2		3,747
Stock options exercised (in shares)		85,136
Stock issued under employee stock purchase plan	5,103			5,103
Stock issued under employee stock purchase plan (in shares)		37,827
Return of common stock to pay withholding taxes on restricted stock	(41,687)	$ (2)	$ (41,685)
Return of common stock to pay withholding taxes on restricted stock (in shares)		164,446	(164,446)
Stock compensation expense	39,781			39,781
Stock repurchase program	$ (84,879)	$ (5)	$ (84,874)
Stock repurchase program, (in shares)	(465,687)	(465,687)	465,687
Other comprehensive income (loss)	$ 3,500					3,500
Net income	203,009				203,009
Ending Balance at Mar. 31, 2020	$ 1,065,466	$ 451	$ (265,411)	739,133	602,482	(11,189)
Ending Balance (in shares) at Mar. 31, 2020	45,008,687	45,008,687	2,533,374
Restricted stock units issued	$ 1	$ 2		(1)
Restricted stock units issued (in shares)		140,159
Stock options exercised	$ 9,075	$ 2		9,073
Stock options exercised (in shares)	215,000	215,262
Stock issued under employee stock purchase plan	$ 5,479			5,479
Stock issued under employee stock purchase plan (in shares)		31,920
Return of common stock to pay withholding taxes on restricted stock	(11,311)	$ (1)	$ (11,310)
Return of common stock to pay withholding taxes on restricted stock (in shares)		57,431	(57,431)
Stock compensation expense	47,006			47,006
Stock repurchase program	$ (11,310)	$ (1)	$ (11,309)
Stock repurchase program, (in shares)	(67,649)	(67,649)	67,649
Other comprehensive income (loss)	$ (256)					(256)
Net income	225,525				225,525
Ending Balance at Mar. 31, 2021	$ 1,329,675	$ 453	$ (288,030)	$ 800,690	$ 828,007	$ (11,445)
Ending Balance (in shares) at Mar. 31, 2021	45,270,948	45,270,948	2,658,454