CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) (USD $)	Total	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net [Member]
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	9,382,937	9,382,937
Common stock repurchases	(141,020,900)		(141,020,900)
Issuance of restricted common stock under stock option plan	1,872,123	1,872,123
Stock option expense	4,863,099	4,863,099
Other comprehensive income	(654,864)			(654,864)
Net income	66,190,438		66,190,438
Balances at Dec. 31, 2012	$ 359,507,846	$ 81,748,912	$ 281,150,232	$ (3,391,298)