Summary of Significant Accounting Policies - Reconciliation of the changes in the allowance for credit losses on contracts (Details 5) (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
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses	$ 3,542,077	$ 3,484,811	$ 3,261,721	$ 3,103,266	$ 2,600,949	$ 3,507,659	$ 3,209,524	$ 3,049,461	$ 13,391,875	$ 12,367,593	$ 15,611,544
Contracts
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				19,499,208				19,952,595	19,499,208	19,952,595	16,383,893
Discounts acquired on new volume
Provision for credit losses									13,252,382	12,185,529	15,485,607
Losses absorbed									(19,851,080)	(14,971,422)	(14,036,888)
Recoveries									3,190,142	2,405,750	2,255,683
Discounts accreted										(73,244)	(135,700)
Balance at end of year	16,090,652				19,499,208				16,090,652	19,499,208	19,952,595
Reported
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses										5,319	4,610,221
Reported | Contracts
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year								35,895,449		35,895,449	30,408,578
Discounts acquired on new volume										12,415,896	12,919,492
Provision for credit losses										(176,745)	4,484,284
Losses absorbed										(14,971,422)	(14,036,888)
Recoveries										2,405,750	2,255,683
Discounts accreted										(73,244)	(135,700)
Balance at end of year					35,495,684					35,495,684	35,895,449
Correction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses										12,362,274	11,001,323
Correction | Contracts
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year								(15,942,854)		(15,942,854)	(14,024,685)
Discounts acquired on new volume										(12,415,896)	(12,919,492)
Provision for credit losses										12,362,274	11,001,323
Losses absorbed
Recoveries
Discounts accreted
Balance at end of year					$ (15,996,476)					$ (15,996,476)	$ (15,942,854)