Income Taxes (Details 1) (USD $)	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Current Income Tax Expense (Benefit) [Abstract]
U.S. Federal									$ 63,140,638	$ 55,179,487	$ 47,303,032
State and local									8,372,748	5,745,452	4,953,995
Foreign									1,629,695	2,247,933	2,580,385
Current income tax expense									73,143,081	63,172,872	54,837,412
Deferred Income Tax Expense (Benefit) [Abstract]
U.S. Federal									(8,792,012)	(2,302,615)	(19,448)
State and local									(857,958)	112,857	(538,793)
Foreign									(1,292,028)	(1,804,216)	(2,279,239)
Deferred income tax benefit									(10,941,998)	(3,993,974)	(2,837,480)
Income Tax Expense (Benefit) [Abstract]
U.S. Federal									54,348,626	52,876,872	47,283,584
State and local									7,514,790	5,858,309	4,415,202
Foreign									337,667	443,717	301,146
Income tax expense reconciliation to U.S. federal tax rate [Abstract]
Expected income tax									58,201,791	55,955,669	50,137,189
Increase (reduction) in income taxes resulting from:
State tax, net of federal benefit									4,884,614	3,807,901	2,869,881
Insurance income exclusion									(123,289)	(118,656)	(165,289)
Uncertain tax positions									283,084	(323,651)	(1,326,568)
Foreign income adjustments									(961,771)	(533,246)	(284,527)
Other, net									(83,346)	390,881	769,246
Income taxes	22,440,000	12,369,000	13,871,000	13,521,000	22,891,000	10,683,000	13,367,000	12,238,000	62,201,083	59,178,898	51,999,932
Deferred tax assets:
Allowance for doubtful accounts	23,078,422				20,536,315				23,078,422	20,536,315
Unearned insurance commissions	13,190,468				13,206,765				13,190,468	13,206,765
Accounts payable and accrued expenses primarily related to employee benefits	8,021,707				6,260,263				8,021,707	6,260,263
Accrued interest receivable	0				2,903,523				0	2,903,523
Reserve for uncollectible interest	5,473,804				0				5,473,804	0
Convertible notes	383,206				563,957				383,206	563,957
Other	728,658				598,041				728,658	598,041
Gross deferred tax assets	50,876,265				44,068,864				50,876,265	44,068,864
Less valuation allowance	(1,274)				(1,274)				(1,274)	(1,274)
Net deferred tax assets	50,874,991				44,067,590				50,874,991	44,067,590
Deferred tax liabilities:
Fair value adjustment for loans	(13,563,946)				(17,243,185)				(13,563,946)	(17,243,185)
Property and equipment	(4,134,286)				(4,397,194)				(4,134,286)	(4,397,194)
Intangible assets	(1,531,635)				(1,534,837)				(1,531,635)	(1,534,837)
Deferred net loan origination fees	(1,728,710)				(1,763,007)				(1,728,710)	(1,763,007)
Prepaid expenses	(500,418)				(654,533)				(500,418)	(654,533)
Unrealized losses	0				(836)				0	(836)
Gross deferred tax liabilities	(21,458,995)				(25,593,592)				(21,458,995)	(25,593,592)
Net deferred tax assets	29,415,996				18,473,998				29,415,996	18,473,998
Reconciliation of the beginning and ending amount of unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits balance at beginning of period				2,704,386					2,704,386
Gross increases for tax positions of current year									221,879
Gross increases for tax positions of prior years									0
Federal and state tax settlements									0
Lapse of statute of limitations									(141,174)
Unrecognized tax benefits balance at end of period	$ 2,785,091				$ 2,704,386				$ 2,785,091	$ 2,704,386