Allowance for Credit Losses - Summary of Allowance for Credit Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Allowance for credit losses and recorded investment in financing receivables
Financing Receivable, Allowance for Credit Losses, Provisions	$ 7	$ 0
Financing Receivable, Allowance for Credit Losses, Recoveries	3	15
Financing Receivable, Allowance for Credit Losses, Charge-offs	(501)	0
Financing Receivable, Allowance for Credit Losses	2,081	2,272	2,572	2,257
Finance Leases Financing Receivable [Member]
Allowance for credit losses and recorded investment in financing receivables
Financing Receivable, Allowance for Credit Losses, Provisions	7	0
Financing Receivable, Allowance for Credit Losses, Recoveries	3	15
Financing Receivable, Allowance for Credit Losses, Charge-offs	(75)	0
Financing Receivable, Allowance for Credit Losses	460	225	525	210
Balance individually evaluated for impairment	89,845	100,819
Notes Receivable [Member]
Allowance for credit losses and recorded investment in financing receivables
Financing Receivable, Allowance for Credit Losses, Provisions	0	0
Financing Receivable, Allowance for Credit Losses, Recoveries	0	0
Financing Receivable, Allowance for Credit Losses, Charge-offs	(426)	0
Financing Receivable, Allowance for Credit Losses	1,621	2,047	2,047	2,047
Balance individually evaluated for impairment	$ 10,842	$ 14,134