Finance Receivables - Internal Credit Quality Rating (Details) $ in Thousands	Mar. 31, 2019 USD ($) tenant	Dec. 31, 2018 USD ($) tenant
Credit Quality Of Finance Receivables
Carrying Value	$ 105,783	$ 105,699
Internally Assigned Grade 1
Credit Quality Of Finance Receivables
Number of tenants and obligors | tenant	0	0
Carrying Value	$ 0	$ 0
Internally Assigned Grade 2
Credit Quality Of Finance Receivables
Number of tenants and obligors | tenant	2	2
Carrying Value	$ 15,685	$ 15,705
Internally Assigned Grade 3
Credit Quality Of Finance Receivables
Number of tenants and obligors | tenant	2	2
Carrying Value	$ 29,759	$ 29,751
Internally Assigned Grade 4
Credit Quality Of Finance Receivables
Number of tenants and obligors | tenant	2	2
Carrying Value	$ 60,339	$ 60,243
Internally Assigned Grade 5
Credit Quality Of Finance Receivables
Number of tenants and obligors | tenant	0	0
Carrying Value	$ 0	$ 0