Receivables (Installment Receivables by Class) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Total Installment Receivables
Non-Impaired installment receivables with no related allowance recorded	$ 889	$ 923
Impaired installment receivables with a related allowance recorded	3,411	3,568
Total installment receivables	4,300	4,491
Unpaid Principal Balance
Non-Impaired installment receivables with no related allowance recorded	856	885
Impaired installment receivables with a related allowance recorded	3,411	3,568
Total installment receivables	4,267	4,453
Non-Impaired Financing Receivable, Related Allowance	0	0
Related Allowance for Doubtful Accounts
Impaired installment receivables with a related allowance recorded	2,569	2,644
Interest Income Recognized
Non-Impaired installment receivables with no related allowance recorded	25	74
Impaired installment receivables with a related allowance recorded	0	0
Total installment receivables	25	74
U.S.
Total Installment Receivables
Impaired installment receivables with a related allowance recorded	3,411	3,566
Unpaid Principal Balance
Impaired installment receivables with a related allowance recorded	3,411	3,566
Related Allowance for Doubtful Accounts
Impaired installment receivables with a related allowance recorded	2,569	2,642
Interest Income Recognized
Impaired installment receivables with a related allowance recorded	0	0
CANADA
Total Installment Receivables
Non-Impaired installment receivables with no related allowance recorded	889	923
Impaired installment receivables with a related allowance recorded	0	2
Total installment receivables	889	925
Unpaid Principal Balance
Non-Impaired installment receivables with no related allowance recorded	856	885
Impaired installment receivables with a related allowance recorded	0	2
Total installment receivables	856	887
Non-Impaired Financing Receivable, Related Allowance	0	0
Related Allowance for Doubtful Accounts
Impaired installment receivables with a related allowance recorded	0	2
Interest Income Recognized
Non-Impaired installment receivables with no related allowance recorded	25	74
Impaired installment receivables with a related allowance recorded	0	0
Total installment receivables	$ 25	$ 74