CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) (USD $)	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net [Member]	Total
Balances at Mar. 31, 2011	$ 47,352,738	$ 395,086,232	$ 136,199	$ 442,575,169
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	65,630,753	355,980,694	(2,736,434)	418,875,013
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Proceeds from exercise of stock options, including tax benefits	4,454,923			4,454,923
Common stock repurchases		(75,141,185)		(75,141,185)
Issuance of restricted common stock under stock option plan	1,317,205			1,317,205
Stock option expense	2,493,015			2,493,015
Other comprehensive income			(125,489)	(125,489)
Net income		45,516,447		45,516,447
Balances at Sep. 30, 2012	$ 73,895,896	$ 326,355,956	$ (2,861,923)	$ 397,389,929