Finance Receivables - Summary of reconciliation of the changes in the allowance for credit losses on contracts (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
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
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