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)	(8,112)
Net income	185,056
Ending Balance at Dec. 31, 2018	851,530	$ 451	$ (138,289)	676,171	325,513	(12,316)
Ending Balance (in shares) at Dec. 31, 2018		45,058,049	1,901,604
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
Restricted stock units issued		$ 1		(1)
Restricted stock units issued (in shares)		14,085
Stock options exercised	429			429
Stock options exercised (in shares)		10,039
Stock issued to directors	33			33
Stock issued to directors (in shares)		103
Return of common stock to pay withholding taxes on restricted stock	(1,546)		$ (1,546)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(4,633)	4,633
Stock issued under employee stock purchase plan (in shares)		2
Stock compensation expense	15,578			15,578
Other comprehensive income (loss)	(781)					(781)
Net income	44,862				44,862
Ending Balance at Dec. 31, 2018	851,530	$ 451	$ (138,289)	676,171	325,513	(12,316)
Ending Balance (in shares) at Dec. 31, 2018		45,058,049	1,901,604
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)	65,000
Stock repurchase program	$ (59,900)
Stock repurchase program (in shares)	(318,361)
Other comprehensive income (loss)	$ (2,306)
Net income	171,211
Ending Balance at Dec. 31, 2019	$ 1,046,863	$ 451	$ (240,330)	733,054	570,683	(16,995)
Ending Balance (in shares) at Dec. 31, 2019	45,112,835	45,112,835	2,385,550
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)
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
Restricted stock units issued (in shares)		6,004
Stock options exercised	460			460
Stock options exercised (in shares)		7,470
Return of common stock to pay withholding taxes on restricted stock	(403)		$ (403)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(2,159)	2,159
Stock compensation expense	10,574			10,574
Stock repurchase program	$ (25,002)	$ (1)	$ (25,001)
Stock repurchase program (in shares)	(137,432)	137,432	(137,432)
Other comprehensive income (loss)	$ 561					561
Net income	69,217				69,217
Ending Balance at Dec. 31, 2019	$ 1,046,863	$ 451	$ (240,330)	$ 733,054	$ 570,683	$ (16,995)
Ending Balance (in shares) at Dec. 31, 2019	45,112,835	45,112,835	2,385,550