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		252,000
Stock issued under employee stock purchase plan, shares		4,228
Stock issued under stock option plan, net of shares repurchased	3,284,000		3,284,000
Stock issued under stock option plan, net of shares repurchased, shares		109,218
Stock-based compensation expense	2,087,000		2,087,000
Purchase of treasury stock	(11,302,000)			$ (11,302,000)
Purchase of treasury stock, shares				(199,978)
Net income	24,567,000				24,567,000
Ending balance at Sep. 30, 2018	190,064,000	$ 3,000	149,328,000	$ (442,291,000)	483,024,000
Ending balance, shares at Sep. 30, 2018		53,907,432		(35,081,057)
Beginning balance at Jun. 30, 2018	181,865,000	$ 3,000	146,102,000	$ (434,475,000)	470,235,000
Beginning balance, shares at Jun. 30, 2018		53,839,539		(34,947,632)
Stock issued under employee stock purchase plan	252,000		252,000
Stock issued under employee stock purchase plan, shares		4,228
Stock issued under stock option plan, net of shares repurchased	2,066,000		2,066,000
Stock issued under stock option plan, net of shares repurchased, shares		63,665
Stock-based compensation expense	908,000		908,000
Purchase of treasury stock	(7,816,000)			$ (7,816,000)
Purchase of treasury stock, shares				(133,425)
Net income	12,789,000				12,789,000
Ending balance at Sep. 30, 2018	190,064,000	$ 3,000	149,328,000	$ (442,291,000)	483,024,000
Ending balance, shares at Sep. 30, 2018		53,907,432		(35,081,057)
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		239,000
Stock issued under employee stock purchase plan, shares		3,323
Stock issued under stock option plan, net of shares repurchased	5,387,000		5,387,000
Stock issued under stock option plan, net of shares repurchased, shares		152,176
Stock-based compensation expense	2,423,000		2,423,000
Purchase of treasury stock	$ (28,316,000)			$ (28,316,000)
Purchase of treasury stock, shares	(348,877)			(348,877)
Net income	$ 26,278,000				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		239,000
Stock issued under employee stock purchase plan, shares		3,323
Stock issued under stock option plan, net of shares repurchased	1,888,000		1,888,000
Stock issued under stock option plan, net of shares repurchased, shares		55,993
Stock-based compensation expense	1,198,000		1,198,000
Purchase of treasury stock	$ (19,197,000)			$ (19,197,000)
Purchase of treasury stock, shares	(224,466)			(224,466)
Net income	$ 12,871,000				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)