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, 2018	$ 171,176,000	$ 3,000	$ 143,705,000	$ (430,989,000)	$ 458,457,000
Beginning balance, shares at Mar. 31, 2018		53,793,986		(34,881,079)
Stock issued under employee stock purchase plan	252,000	$ 0	252,000	$ 0	0
Stock issued under employee stock purchase plan, shares		4,228
Stock issued under stock option plan, net of shares repurchased	5,456,000	$ 0	5,456,000	0	0
Stock issued under stock option plan, net of shares repurchased, shares		169,448
Stock-based compensation expense	3,110,000	$ 0	3,110,000	0	0
Purchase of treasury stock	(22,591,000)	0	0	$ (22,591,000)	0
Purchase of treasury stock, shares				(386,552)
Net income	34,865,000	0	0	$ 0	34,865,000
Ending balance at Dec. 31, 2018	192,268,000	$ 3,000	152,523,000	$ (453,580,000)	493,322,000
Ending balance, shares at Dec. 31, 2018		53,967,662		(35,267,631)
Beginning balance at Sep. 30, 2018	190,064,000	$ 3,000	149,328,000	$ (442,291,000)	483,024,000
Beginning balance, shares at Sep. 30, 2018		53,907,432		(35,081,057)
Stock issued under stock option plan, net of shares repurchased	2,172,000	$ 0	2,172,000	$ 0	0
Stock issued under stock option plan, net of shares repurchased, shares		60,230
Stock-based compensation expense	1,023,000	$ 0	1,023,000	0	0
Purchase of treasury stock	(11,289,000)	0	0	$ (11,289,000)	0
Purchase of treasury stock, shares				(186,574)
Net income	10,298,000	0	0	$ 0	10,298,000
Ending balance at Dec. 31, 2018	192,268,000	$ 3,000	152,523,000	$ (453,580,000)	493,322,000
Ending balance, shares at Dec. 31, 2018		53,967,662		(35,267,631)
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)			(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)			(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)