CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
Stockholders' equity, beginning of period at Mar. 31, 2012	$ 527,244	$ 741	$ 557,218	$ 6,357	$ 115,358	$ (152,430)
Common stock, shares, beginning of period at Mar. 31, 2012		42,512,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	106,402				106,402
Foreign currency translation adjustments	(261)			(261)
Net unrealized gains (losses) on cash flow hedges, net of tax	(555)			(555)
Net unrealized gains on investments, net of tax	26			26
Proceeds from issuances under stock-based compensation plans, shares		1,730,000
Proceeds from issuances under stock-based compensation plans	31,865	16	29,289			2,560
Repurchase of restricted common stock, shares		(114,000)
Repurchase of restricted common stock	0	0
Cash dividends	(17,072)				(17,072)
Stock-based compensation	18,350		18,350
Tax benefit from stock-based awards	1,260		1,260
Repurchase of common stock, shares		(752,000)
Repurchase of common stock	(23,931)					(23,931)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(93,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(3,047)					(3,047)
Adjustment related to expired stock options	6,166		6,166
Retirement of treasury stock	0				(176,344)	176,344
Stockholders' equity, end of period at Mar. 31, 2013	646,447	757	612,283	5,567	28,344	(504)
Common stock, shares, end of period at Mar. 31, 2013		43,283,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	112,417				112,417
Foreign currency translation adjustments	(244)			(244)
Net unrealized gains (losses) on cash flow hedges, net of tax	(2,760)			(2,760)
Net unrealized gains on investments, net of tax	75			75
Proceeds from issuances under stock-based compensation plans, shares		1,498,000
Proceeds from issuances under stock-based compensation plans	24,055	14	24,041			0
Repurchase of restricted common stock, shares		(45,000)
Repurchase of restricted common stock	0	0
Cash dividends	(17,372)				(17,372)
Stock-based compensation	23,180		23,180
Tax benefit from stock-based awards	4,659		4,659
Repurchase of common stock, shares		(1,949,000)
Repurchase of common stock	(85,654)					(85,654)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(138,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(6,222)	(1)				(6,221)
Other equity changes related to compensation	83		(680)			763
Stockholders' equity, end of period at Mar. 31, 2014	698,664	770	663,483	2,638	123,389	(91,616)
Common stock, shares, end of period at Mar. 31, 2014		42,649,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	112,301				112,301
Foreign currency translation adjustments	476			476
Net unrealized gains (losses) on cash flow hedges, net of tax	7,004			7,004
Net unrealized gains on investments, net of tax	2			2
Proceeds from issuances under stock-based compensation plans, shares		1,418,000
Proceeds from issuances under stock-based compensation plans	23,042	15	23,027			0
Repurchase of restricted common stock, shares		(80,000)
Repurchase of restricted common stock	0	0
Cash dividends	(25,730)				(25,730)
Stock-based compensation	28,594		28,594
Tax benefit from stock-based awards	3,378		3,378
Repurchase of common stock, shares		(2,221,000)
Repurchase of common stock	(112,939)					(112,939)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(165,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(7,611)	(2)				(7,609)
Other equity changes related to compensation	216		(634)			850
Stockholders' equity, end of period at Mar. 31, 2015	$ 727,397	$ 783	$ 717,848	$ 10,120	$ 209,960	$ (211,314)
Common stock, shares, end of period at Mar. 31, 2015		41,601,000