Consolidated Statements of Stockholders' Equity and Comprehensive Income (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common stock Voting	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Treasury stock	Retained Earnings
Beginning Balance at Mar. 31, 2012	$ 342,369	$ 48	$ 237,289	$ 212	$ (56,032)	$ 160,852
Beginning Balance (in shares) at Mar. 31, 2012		48,185,731			6,371,540
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,609					40,609
Unrealized net investment gains (losses)	109			109
Unrealized net gains (losses) on derivative financial instruments	(110)			(110)
Cumulative translation adjustments	460			460
Issuance of common stock pursuant to exercise of options	574	0	574
Issuance of common stock pursuant to exercise of options (in shares)	86,892	86,892
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		549,932
Stock-based compensation expense for restricted stock units granted to employees	8,887		8,887
Issuance of common stock under employee stock purchase plan	4,545		4,545
Issuance of common stock under employee stock purchase plan (in shares)		184,936
Repurchase of treasury stock	(27,448)				(27,448)
Repurchase of treasury stock (in shares)					1,169,030
Tax benefits of disqualifying dispositions of incentive stock options	1,907		1,907
Ending Balance at Mar. 31, 2013	371,903	49	253,202	671	(83,480)	201,461
Ending Balance (in shares) at Mar. 31, 2013		49,007,491			7,540,570
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	49,106					49,106
Unrealized net investment gains (losses)	5			5
Unrealized net gains (losses) on derivative financial instruments	209			209
Cumulative translation adjustments	1,887			1,887
Issuance of common stock pursuant to exercise of options	811	0	811
Issuance of common stock pursuant to exercise of options (in shares)	117,650	117,650
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		635,254
Stock-based compensation expense for restricted stock units granted to employees	12,178		12,178
Issuance of common stock under employee stock purchase plan	4,995		4,995
Issuance of common stock under employee stock purchase plan (in shares)		162,564
Repurchase of treasury stock	(34,322)				(34,322)
Repurchase of treasury stock (in shares)					1,216,605
Tax benefits of disqualifying dispositions of incentive stock options	2,388		2,388
Ending Balance at Mar. 31, 2014	409,161	50	273,574	2,772	(117,802)	250,567
Ending Balance (in shares) at Mar. 31, 2014		49,922,959			8,757,175
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	61,192					61,192
Unrealized net investment gains (losses)	(12)			(12)
Unrealized net gains (losses) on derivative financial instruments	(1,094)			(1,094)
Cumulative translation adjustments	(6,311)			(6,311)
Issuance of common stock pursuant to exercise of options	139	0	139
Issuance of common stock pursuant to exercise of options (in shares)	23,850	23,850
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		728,239
Stock-based compensation expense for restricted stock units granted to employees	15,685		15,685
Issuance of common stock under employee stock purchase plan	5,889		5,889
Issuance of common stock under employee stock purchase plan (in shares)		137,500
Repurchase of treasury stock	(51,714)				(51,714)
Repurchase of treasury stock (in shares)					1,247,568
Tax benefits of disqualifying dispositions of incentive stock options	2,814		2,814
Ending Balance at Mar. 31, 2015	$ 435,750	$ 51	$ 298,101	$ (4,645)	$ (169,516)	$ 311,759
Ending Balance (in shares) at Mar. 31, 2015		50,812,548			10,004,743