CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $)	Total	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net [Member]
Balances at Mar. 31, 2010	$ 382,947,954	$ 27,112,822	$ 357,179,568	$ (1,344,436)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Proceeds from exercise of stock options, including tax benefits	13,806,260	13,806,260
Common stock repurchases	(53,342,516)		(53,342,516)
Issuance of restricted common stock under stock option plan	1,485,359	1,485,359
Stock option expense	3,855,348	3,855,348
Repurchase and cancellation of convertible notes	1,092,949	1,092,949
Other comprehensive income	1,480,635			1,480,635
Net income	91,249,180		91,249,180
Balances at Mar. 31, 2011	442,575,169	47,352,738	395,086,232	136,199
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Proceeds from exercise of stock options, including tax benefits	11,660,188	11,660,188
Common stock repurchases	(139,799,981)		(139,799,981)
Issuance of restricted common stock under stock option plan	1,750,596	1,750,596
Stock option expense	4,867,231	4,867,231
Other comprehensive income	(2,872,633)			(2,872,633)
Net income	100,694,443		100,694,443
Balances at Mar. 31, 2012	418,875,013	65,630,753	355,980,694	(2,736,434)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Proceeds from exercise of stock options, including tax benefits	12,993,709	12,993,709
Common stock repurchases	(183,045,655)		(183,045,655)
Issuance of restricted common stock under stock option plan	3,842,674	3,842,674
Stock option expense	7,322,653	7,322,653
Other comprehensive income	2,318,117			2,318,117
Net income	104,089,748		104,089,748
Balances at Mar. 31, 2013	$ 366,396,259	$ 89,789,789	$ 277,024,787	$ (418,317)