Consolidated Statements of Stockholders' Equity - Unaudited - USD ($)	Total	Common Stock [Member]	Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]
Beginning balance at Mar. 31, 2019	$ 194,805,000	$ 3,000	$ 155,798,000	$ (466,156,000)	$ 505,160,000
Beginning balance, shares at Mar. 31, 2019		54,021,032		(35,463,238)
Stock issued under employee stock purchase plan	239,000	$ 0	239,000	$ 0	0
Stock issued under employee stock purchase plan, shares		3,323
Stock issued under stock option plan, net of shares repurchased	5,387,000	$ 0	5,387,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		152,176
Stock-based compensation expense	2,423,000	$ 0	2,423,000	0	0
Purchase of treasury stock	(28,316,000)	0	0	$ (28,316,000)	0
Purchase of treasury stock, shares				(348,877)
Net income	26,278,000	0	0	$ 0	26,278,000
Ending balance at Sep. 30, 2019	200,816,000	$ 3,000	163,847,000	$ (494,472,000)	531,438,000
Ending balance, shares at Sep. 30, 2019		54,176,531		(35,812,115)
Beginning balance at Jun. 30, 2019	203,817,000	$ 3,000	160,522,000	$ (475,275,000)	518,567,000
Beginning balance, shares at Jun. 30, 2019		54,117,215		(35,587,649)
Stock issued under employee stock purchase plan	239,000	$ 0	239,000	$ 0	0
Stock issued under employee stock purchase plan, shares		3,323
Stock issued under stock option plan, net of shares repurchased	1,888,000	$ 0	1,888,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		55,993
Stock-based compensation expense	1,198,000	$ 0	1,198,000	0	0
Purchase of treasury stock	(19,197,000)	0	0	$ (19,197,000)	0
Purchase of treasury stock, shares				(224,466)
Net income	12,871,000	0	0	$ 0	12,871,000
Ending balance at Sep. 30, 2019	200,816,000	$ 3,000	163,847,000	$ (494,472,000)	531,438,000
Ending balance, shares at Sep. 30, 2019		54,176,531		(35,812,115)
Beginning balance at Mar. 31, 2020	189,711,000	$ 3,000	168,935,000	$ (531,764,000)	552,537,000
Beginning balance, shares at Mar. 31, 2020		54,254,557		(36,285,591)
Stock issued under employee stock purchase plan	257,000	$ 0	257,000	$ 0	0
Stock issued under employee stock purchase plan, shares		3,173
Stock issued under stock option plan, net of shares repurchased	4,472,000	$ 0	4,472,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		121,162
Stock-based compensation expense	2,233,000	$ 0	2,233,000	0	0
Purchase of treasury stock	$ (14,440,000)	0	0	$ (14,440,000)	0
Purchase of treasury stock, shares	(184,963)			(184,963)
Net income	$ 20,167,000	0	0	$ 0	20,167,000
Ending balance at Sep. 30, 2020	202,400,000	$ 3,000	175,897,000	$ (546,204,000)	572,704,000
Ending balance, shares at Sep. 30, 2020		54,378,892		(36,470,554)
Beginning balance at Jun. 30, 2020	198,092,000	$ 3,000	171,412,000	$ (534,162,000)	560,839,000
Beginning balance, shares at Jun. 30, 2020		54,296,812		(36,320,229)
Stock issued under employee stock purchase plan	257,000	$ 0	257,000	$ 0	0
Stock issued under employee stock purchase plan, shares		3,173
Stock issued under stock option plan, net of shares repurchased	2,990,000	$ 0	2,990,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		78,907
Stock-based compensation expense	1,238,000	$ 0	1,238,000	0	0
Purchase of treasury stock	$ (12,042,000)	0	0	$ (12,042,000)	0
Purchase of treasury stock, shares	(150,325)			(150,325)
Net income	$ 11,865,000	0	0	$ 0	11,865,000
Ending balance at Sep. 30, 2020	$ 202,400,000	$ 3,000	$ 175,897,000	$ (546,204,000)	$ 572,704,000
Ending balance, shares at Sep. 30, 2020		54,378,892		(36,470,554)