CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
Common stock, shares, beginning of period at Mar. 31, 2015		41,601,000
Stockholders' equity, beginning of period at Mar. 31, 2015	$ 727,397	$ 783	$ 717,848	$ 10,120	$ 209,960	$ (211,314)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	68,392				68,392
Foreign currency translation adjustments	376			376
Net unrealized gains (losses) on cash flow hedges, net of tax	(6,680)			(6,680)
Net unrealized gains (losses) on investments, net of tax	(57)			(57)
Proceeds from issuances under stock-based compensation plans, shares		1,155,000
Proceeds from issuances under stock-based compensation plans	15,384	$ 10	15,374
Repurchase of restricted common stock, shares		(158,000)
Repurchase of restricted common stock	0	$ 0
Cash dividends	(21,061)				(21,061)
Stock-based compensation	33,265		33,265
Tax benefit from stock-based awards	3,515		3,515
Repurchase of common stock, shares		(9,077,000)
Repurchase of common stock	(497,393)					(497,393)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(201,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(11,068)	$ 0				(11,068)
Other equity changes related to compensation	329		(513)			842
Common stock, shares, end of period at Mar. 31, 2016		33,320,000
Stockholders' equity, end of period at Mar. 31, 2016	312,399	$ 793	769,489	3,759	257,291	(718,933)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	82,599				82,599
Foreign currency translation adjustments	(311)			(311)
Net unrealized gains (losses) on cash flow hedges, net of tax	1,616			1,616
Net unrealized gains (losses) on investments, net of tax	(370)			(370)
Proceeds from issuances under stock-based compensation plans, shares		1,125,000
Proceeds from issuances under stock-based compensation plans	15,204	$ 11	15,193
Repurchase of restricted common stock, shares		(47,000)
Repurchase of restricted common stock	0	$ 0
Cash dividends	(19,959)				(19,959)
Stock-based compensation	33,539		33,539
Tax benefit from stock-based awards	546		546
Repurchase of common stock, shares		(764,000)
Repurchase of common stock	(34,236)					(34,236)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(218,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(9,736)	$ 0				(9,736)
Other equity changes related to compensation	865		10			855
Common stock, shares, end of period at Mar. 31, 2017		33,416,000
Stockholders' equity, end of period at Mar. 31, 2017	382,156	$ 804	818,777	4,694	319,931	(762,050)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(869)				(869)
Foreign currency translation adjustments	257			257
Net unrealized gains (losses) on cash flow hedges, net of tax	(2,190)			(2,190)
Net unrealized gains (losses) on investments, net of tax	109			109
Proceeds from issuances under stock-based compensation plans, shares		1,288,000
Proceeds from issuances under stock-based compensation plans	23,927	$ 12	23,915
Repurchase of restricted common stock, shares		(98,000)
Repurchase of restricted common stock	0	$ 0
Cash dividends	(19,996)				(19,996)
Stock-based compensation	33,959		33,959
Tax benefit from stock-based awards	$ 0
Repurchase of common stock, shares	(1,139,548)	(1,140,000)
Repurchase of common stock	$ (52,948)					(52,948)
Employees' tax withheld and paid for restricted stock and restricted stock units, shares		(215,000)
Employees' tax withheld and paid for restricted stock and restricted stock units	(11,429)	$ 0				(11,429)
Other equity changes related to compensation	(6)		(6)
Common stock, shares, end of period at Mar. 31, 2018		33,251,000
Stockholders' equity, end of period at Mar. 31, 2018	$ 352,970	$ 816	$ 876,645	$ 2,870	$ 299,066	$ (826,427)