Finance Receivables - Internal Credit Quality Rating (Details) $ in Thousands	Dec. 31, 2016 USD ($) tenant	Dec. 31, 2015 USD ($) tenant
Credit Quality Of Finance Receivables
Net investments in direct financing leases	$ 694,410	$ 767,036
Internally Assigned Grade1 thru 3
Credit Quality Of Finance Receivables
Number of tenants | tenant	27	28
Net investments in direct financing leases	$ 621,955	$ 657,034
Internally Assigned Grade 4
Credit Quality Of Finance Receivables
Number of tenants | tenant	5	6
Net investments in direct financing leases	$ 70,811	$ 110,002
Internally Assigned Grade 5
Credit Quality Of Finance Receivables
Number of tenants | tenant	1	0
Net investments in direct financing leases	$ 1,644	$ 0