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	6,637,000	$ 0	6,637,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		180,401
Stock-based compensation expense	3,566,000	$ 0	3,566,000	0	0
Purchase of treasury stock	(47,512,000)	0	0	$ (47,512,000)	0
Purchase of treasury stock, shares				(588,903)
Net income	35,630,000	0	0	$ 0	35,630,000
Ending balance at Dec. 31, 2019	193,365,000	$ 3,000	166,240,000	$ (513,668,000)	540,790,000
Ending balance, shares at Dec. 31, 2019		54,204,756		(36,052,141)
Beginning balance at Sep. 30, 2019	200,816,000	$ 3,000	163,847,000	$ (494,472,000)	531,438,000
Beginning balance, shares at Sep. 30, 2019		54,176,531		(35,812,115)
Stock issued under stock option plan, net of shares repurchased	1,250,000	$ 0	1,250,000	$ 0	0
Stock issued under stock option plan, net of shares repurchased, shares		28,225
Stock-based compensation expense	1,143,000	$ 0	1,143,000	0	0
Purchase of treasury stock	(19,196,000)	0	0	$ (19,196,000)	0
Purchase of treasury stock, shares				(240,026)
Net income	9,352,000	0	0	$ 0	9,352,000
Ending balance at Dec. 31, 2019	193,365,000	$ 3,000	166,240,000	$ (513,668,000)	540,790,000
Ending balance, shares at Dec. 31, 2019		54,204,756		(36,052,141)
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	6,999,000	$ 0	6,999,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		182,024
Stock-based compensation expense	3,484,000	$ 0	3,484,000	0	0
Purchase of treasury stock	$ (22,125,000)	0	0	$ (22,125,000)	0
Purchase of treasury stock, shares	(267,120)			(267,120)
Net income	$ 31,547,000	0	0	$ 0	31,547,000
Ending balance at Dec. 31, 2020	209,873,000	$ 3,000	179,675,000	$ (553,889,000)	584,084,000
Ending balance, shares at Dec. 31, 2020		54,439,754		(36,552,711)
Beginning balance at Sep. 30, 2020	202,400,000	$ 3,000	175,897,000	$ (546,204,000)	572,704,000
Beginning balance, shares at Sep. 30, 2020		54,378,892		(36,470,554)
Stock issued under stock option plan, net of shares repurchased	2,527,000	$ 0	2,527,000	$ 0	0
Stock issued under stock option plan, net of shares repurchased, shares		60,862
Stock-based compensation expense	1,251,000	$ 0	1,251,000	0	0
Purchase of treasury stock	$ (7,685,000)	0	0	$ (7,685,000)	0
Purchase of treasury stock, shares	(82,157)			(82,157)
Net income	$ 11,380,000	0	0	$ 0	11,380,000
Ending balance at Dec. 31, 2020	$ 209,873,000	$ 3,000	$ 179,675,000	$ (553,889,000)	$ 584,084,000
Ending balance, shares at Dec. 31, 2020		54,439,754		(36,552,711)