Consolidated Stockholders' Equity - Unaudited - USD ($)	Total	Common Stock [Member]	Paid-in-Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]
Beginning balance at Mar. 31, 2017	$ 138,646,000	$ 3,000	$ 135,683,000	$ (419,802,000)	$ 422,762,000
Beginning balance, shares at Mar. 31, 2017		53,569,067		(34,631,834)
Stock issued under employee stock purchase plan	223,000		223,000
Stock issued under employee stock purchase plan, shares		4,319
Stock issued under stock option plan, net of shares repurchased	2,404,000		2,404,000
Stock issued under stock option plan, net of shares repurchased, shares		173,717
Stock-based compensation expense	2,382,000		2,382,000
Adjustment to deferred income taxes for prior year's stock options	975,000		975,000
Purchase of treasury stock	(11,187,000)			$ (11,187,000)
Purchase of treasury stock, shares				(249,245)
Net income	26,737,000				26,737,000
Ending balance at Dec. 31, 2017	160,180,000	$ 3,000	141,667,000	$ (430,989,000)	449,499,000
Ending balance, shares at Dec. 31, 2017		53,747,103		(34,881,079)
Beginning balance at Sep. 30, 2017	147,696,000	$ 3,000	138,752,000	$ (430,989,000)	439,930,000
Beginning balance, shares at Sep. 30, 2017		53,706,008		(34,881,079)
Stock issued under employee stock purchase plan	(8,000)		(8,000)
Stock issued under stock option plan, net of shares repurchased	1,096,000		1,096,000
Stock issued under stock option plan, net of shares repurchased, shares		41,095
Stock-based compensation expense	852,000		852,000
Adjustment to deferred income taxes for prior year's stock options	975,000		975,000
Net income	9,569,000				9,569,000
Ending balance at Dec. 31, 2017	160,180,000	$ 3,000	141,667,000	$ (430,989,000)	449,499,000
Ending balance, shares at Dec. 31, 2017		53,747,103		(34,881,079)
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	5,456,000		5,456,000
Stock issued under stock option plan, net of shares repurchased, shares		169,448
Stock-based compensation expense	3,110,000		3,110,000
Purchase of treasury stock	$ (22,591,000)			$ (22,591,000)
Purchase of treasury stock, shares	(386,552)			(386,552)
Net income	$ 34,865,000				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		2,172,000
Stock issued under stock option plan, net of shares repurchased, shares		60,230
Stock-based compensation expense	1,023,000		1,023,000
Purchase of treasury stock	$ (11,289,000)			$ (11,289,000)
Purchase of treasury stock, shares	(186,574)			(186,574)
Net income	$ 10,298,000				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)