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, 2011	$ 319,559	$ 47	$ 227,201	$ (676)	$ (35,437)	$ 128,424
Beginning Balance (in shares) at Mar. 31, 2011		47,441,879			4,884,658
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,428					32,428
Unrealized net investment gains	1,357			1,357
Unrealized net losses on derivative financial instruments	(84)			(84)
Cumulative translation adjustments	(385)			(385)
Issuance of common stock pursuant to exercise of options (in shares)	84,502	84,502
Issuance of common stock pursuant to exercise of options	472	0	472
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		659,350
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Stock-based compensation expense for restricted stock units granted to employees	8,651		8,651
Repurchase of treasury stock (in shares)					1,486,882
Repurchase of treasury stock	(20,595)				(20,595)
Tax benefits of disqualifying dispositions of incentive stock options	965		965
Ending Balance at Mar. 31, 2012	342,369	48	237,289	212	(56,032)	160,852
Ending 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	109			109
Unrealized net losses on derivative financial instruments	(110)			(110)
Cumulative translation adjustments	460			460
Issuance of common stock pursuant to exercise of options (in shares)	86,892	86,892
Issuance of common stock pursuant to exercise of options	574	0	574
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		549,932
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Stock-based compensation expense for restricted stock units granted to employees	8,887		8,887
Issuance of common stock under employee stock purchase plan (in shares)		184,936
Issuance of common stock under employee stock purchase plan	4,545		4,545
Repurchase of treasury stock (in shares)					1,169,030
Repurchase of treasury stock	(27,448)				(27,448)
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	5			5
Unrealized net losses on derivative financial instruments	209			209
Cumulative translation adjustments	1,887			1,887
Issuance of common stock pursuant to exercise of options (in shares)	117,650	117,650
Issuance of common stock pursuant to exercise of options	811	0	811
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		635,254
Issuance of common stock pursuant to vesting of restricted stock units	1	1
Stock-based compensation expense for restricted stock units granted to employees	12,178		12,178
Issuance of common stock under employee stock purchase plan (in shares)		162,564
Issuance of common stock under employee stock purchase plan	4,995		4,995
Repurchase of treasury stock (in shares)					1,216,605
Repurchase of treasury stock	(34,322)				(34,322)
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