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, 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)		384,887
Stock options exercised	5,798	$ 3		5,795
Stock options exercised (in shares)		282,368
Stock issued to directors	33			33
Stock issued to directors (in shares)		80
Return of common stock to pay withholding taxes on restricted stock	(67,598)	$ (2)	$ (67,596)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(166,401)	166,401
Stock compensation expense	12,245			12,245
Other comprehensive income (loss)	(6,709)					(6,709)
Net income	90,066				90,066
Ending Balance at Jun. 30, 2018	723,359	$ 449	$ (134,674)	637,974	230,523	(10,913)
Ending Balance (in shares) at Jun. 30, 2018		44,876,271	1,891,713
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
Other comprehensive income (loss)	(7,331)
Net income	140,193
Ending Balance at Sep. 30, 2018	792,954	$ 450	$ (136,743)	660,132	280,650	(11,535)
Ending Balance (in shares) at Sep. 30, 2018		45,038,453	1,896,971
Beginning Balance at Jun. 30, 2018	723,359	$ 449	$ (134,674)	637,974	230,523	(10,913)
Beginning Balance (in shares) at Jun. 30, 2018		44,876,271	1,891,713
Restricted stock units issued (in shares)		18,827
Stock options exercised	4,815	$ 1		4,814
Stock options exercised (in shares)		142,978
Stock issued to directors	34			34
Stock issued to directors (in shares)		74
Return of common stock to pay withholding taxes on restricted stock	(2,069)		$ (2,069)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(5,258)	5,258
Stock issued under employee stock purchase plan	1,376			1,376
Stock issued under employee stock purchase plan (in shares)		5,561
Stock compensation expense	15,934			15,934
Other comprehensive income (loss)	(622)					(622)
Net income	50,127				50,127
Ending Balance at Sep. 30, 2018	792,954	$ 450	$ (136,743)	660,132	280,650	(11,535)
Ending Balance (in shares) at Sep. 30, 2018		45,038,453	1,896,971
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	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	45,122,985	1,903,241
Stock options exercised (in shares)	58,000
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	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 (in 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	45,238,952	2,245,959