Consolidated Statements of Stockholders' Equity and Comprehensive Income (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Retained Earnings
Beginning Balance at Mar. 31, 2010	$ 266,843	$ 46	$ 209,146	$ (1,817)	$ (31,691)	$ 91,159
Beginning Balance (in shares) at Mar. 31, 2010		46,490,166			4,720,584
Net income	37,265					37,265
Unrealized net investment gains	936			936
Unrealized net gains on derivative financial instruments	205			205
Cumulative translation adjustments	0
Issuance of common stock pursuant to exercise of options (in shares)	450,432	450,432
Issuance of common stock pursuant to exercise of options	3,379	1	3,378
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		501,281			164,074
Issuance of common stock pursuant to vesting of restricted stock units	(3,746)	0			(3,746)
Stock-based compensation expense for restricted stock units granted to employees	6,439		6,439
Tax benefits of disqualifying dispositions of incentive stock options	8,238		8,238
Ending Balance at Mar. 31, 2011	319,559	47	227,201	(676)	(35,437)	128,424
Ending Balance (in shares) at Mar. 31, 2011		47,441,879			4,884,658
Net income	32,428					32,428
Unrealized net investment gains	1,357			1,357
Unrealized net gains 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
Net income	40,609					40,609
Unrealized net investment gains	109			109
Unrealized net gains 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