Net Investment in Sales-Type Leases allowance credit loss rollforward (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Net Investment in Sales-Type Leases [Abstract]
Allowance for Notes, Loans and Financing Receivable, Current	$ 100,000		$ 500,000
Allowance for Notes, Loans and Financing Receivable, Noncurrent	100,000		100,000
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for credit losses, beginning of period	607,000	284,000
Current period provision (reversal)	13,000	0
Direct write-downs charged against the allowance	(413,000)	0
Recoveries of amounts previously charged off	(17,000)	(27,000)
Allowance for credit losses, end of period	$ 190,000	$ 257,000