Allowance for Credit Losses - Summary of Allowance for Credit Losses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Allowance for credit losses and recorded investment in financing receivables
Balance January 1, 2011	$ 2,257	$ 848
Provision for credit losses	263	2,185
Recoveries	52	5,593
Write-offs	0	(6,369)
Balance December 31, 2011	2,572	2,257
Recorded investment in financing receivables
Allowance resulting from individual impairment evaluation	2,572	2,257
Finance Leases [Member]
Allowance for credit losses and recorded investment in financing receivables
Balance January 1, 2011	210	378
Provision for credit losses	263	107
Recoveries	52	138
Write-offs	0	(413)
Balance December 31, 2011	525	210
Recorded investment in financing receivables
Financing receivables individually evaluated for impairment	78,181	98,506
Notes Receivable [Member]
Allowance for credit losses and recorded investment in financing receivables
Balance January 1, 2011	2,047	470
Provision for credit losses	0	2,078
Recoveries	0	5,455
Write-offs	0	(5,956)
Balance December 31, 2011	2,047	2,047
Recorded investment in financing receivables
Financing receivables individually evaluated for impairment	$ 12,855	$ 13,869