Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Mar. 31, 2019	$ 936,890	$ 451	$ (138,852)	$ 690,507	$ 399,473	$ (14,689)
Beginning 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)		373,430
Stock options exercised	1,261	$ 1		1,260
Stock options exercised (in shares)		36,289
Return of common stock to pay withholding taxes on restricted stock	(40,536)	$ (2)	$ (40,534)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(158,426)	158,426
Stock compensation expense	13,121			13,121
Other comprehensive income (loss)	2,934					2,934
Net income	88,923				88,923
Ending Balance at Jun. 30, 2019	1,002,593	$ 454	$ (179,386)	704,884	488,396	(11,755)
Ending Balance (in shares) at Jun. 30, 2019		45,374,278	2,061,667
Beginning Balance at Mar. 31, 2019	936,890	$ 451	$ (138,852)	690,507	399,473	(14,689)
Beginning Balance (in shares) at Mar. 31, 2019		45,122,985	1,903,241
Stock repurchase program	$ (34,900)
Stock repurchase program, Shares	(180,929)
Other comprehensive income (loss)	$ (2,867)
Net income	101,994
Ending Balance at Sep. 30, 2019	991,457	$ 452	$ (214,926)	722,020	501,467	(17,556)
Ending Balance (in shares) at Sep. 30, 2019		45,238,952	2,245,959
Beginning Balance at Jun. 30, 2019	1,002,593	$ 454	$ (179,386)	704,884	488,396	(11,755)
Beginning Balance (in shares) at Jun. 30, 2019		45,374,278	2,061,667
Restricted stock units issued (in shares)		12,039
Stock options exercised	1,445			1,445
Stock options exercised (in shares)		21,268
Return of common stock to pay withholding taxes on restricted stock	(668)		$ (668)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(3,363)	3,363
Stock issued under employee stock purchase plan	2,368			2,368
Stock issued under employee stock purchase plan (in shares)		15,659
Stock compensation expense	13,323			13,323
Stock repurchase program	$ (34,874)	$ (2)	$ (34,872)
Stock repurchase program, Shares	(180,929)	(180,929)	180,929
Other comprehensive income (loss)	$ (5,801)					(5,801)
Net income	13,071				13,071
Ending Balance at Sep. 30, 2019	991,457	$ 452	$ (214,926)	722,020	501,467	(17,556)
Ending Balance (in shares) at Sep. 30, 2019		45,238,952	2,245,959
Beginning Balance at Mar. 31, 2020	$ 1,065,466	$ 451	$ (265,411)	739,133	602,482	(11,189)
Beginning Balance (in shares) at Mar. 31, 2020	45,008,687	45,008,687	2,533,374
Restricted stock units issued		$ 1		(1)
Restricted stock units issued (in shares)		124,749
Stock options exercised	$ 1,010			1,010
Stock options exercised (in shares)		31,488
Return of common stock to pay withholding taxes on restricted stock	(9,857)		$ (9,857)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(52,515)	52,515
Stock compensation expense	9,298			9,298
Stock repurchase program	(11,310)	$ (1)	$ (11,309)
Stock repurchase program, Shares		(67,649)	67,649
Other comprehensive income (loss)	2,654					2,654
Net income	44,588				44,588
Ending Balance at Jun. 30, 2020	1,101,848	$ 450	$ (286,577)	749,440	647,070	(8,535)
Ending Balance (in shares) at Jun. 30, 2020		45,044,760	2,653,538
Beginning Balance at Mar. 31, 2020	$ 1,065,466	$ 451	$ (265,411)	739,133	602,482	(11,189)
Beginning Balance (in shares) at Mar. 31, 2020	45,008,687	45,008,687	2,533,374
Stock options exercised (in shares)	153,000
Stock repurchase program	$ (11,300)
Stock repurchase program, Shares	(67,649)
Other comprehensive income (loss)	$ 3,990
Net income	106,801
Ending Balance at Sep. 30, 2020	$ 1,182,409	$ 452	$ (287,654)	767,527	709,283	(7,199)
Ending Balance (in shares) at Sep. 30, 2020	45,189,883	45,189,883	2,657,140
Beginning Balance at Jun. 30, 2020	$ 1,101,848	$ 450	$ (286,577)	749,440	647,070	(8,535)
Beginning Balance (in shares) at Jun. 30, 2020		45,044,760	2,653,538
Restricted stock units issued (in shares)		11,554
Stock options exercised	4,545	$ 1		4,544
Stock options exercised (in shares)		121,066
Return of common stock to pay withholding taxes on restricted stock	(1,077)		$ (1,077)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(3,602)	3,602
Stock issued under employee stock purchase plan	1,979	$ 1		1,978
Stock issued under employee stock purchase plan (in shares)		16,105
Stock compensation expense	11,565			11,565
Other comprehensive income (loss)	1,336					1,336
Net income	62,213				62,213
Ending Balance at Sep. 30, 2020	$ 1,182,409	$ 452	$ (287,654)	$ 767,527	$ 709,283	$ (7,199)
Ending Balance (in shares) at Sep. 30, 2020	45,189,883	45,189,883	2,657,140