Allowance for Credit Losses - Summary of Allowance for Credit Losses (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 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	$ 247
Financing Receivable, Allowance for Credit Losses, Recoveries	3	41
Financing Receivable, Allowance for Credit Losses, Charge-offs	(2,137)	0
Financing Receivable, Allowance for Credit Losses	445	2,545	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	247
Financing Receivable, Allowance for Credit Losses, Recoveries	3	41
Financing Receivable, Allowance for Credit Losses, Charge-offs	(90)	0
Financing Receivable, Allowance for Credit Losses	445	498	525	210
Balance individually evaluated for impairment	90,490	95,753
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	(2,047)	0
Financing Receivable, Allowance for Credit Losses	0	2,047	2,047	2,047
Balance individually evaluated for impairment	$ 10,808	$ 13,829