Finance Receivables - Internal Credit Quality Rating (Details) $ in Thousands	Jun. 30, 2017 USD ($) tenant	Dec. 31, 2016 USD ($) tenant
Credit Quality Of Finance Receivables
Net investments in direct financing leases	$ 719,163	$ 694,410
Internally Assigned Grade1-3
Credit Quality Of Finance Receivables
Number of tenants | tenant	25	27
Net investments in direct financing leases	$ 621,252	$ 621,955
Internally Assigned Grade 4
Credit Quality Of Finance Receivables
Number of tenants | tenant	7	5
Net investments in direct financing leases	$ 96,178	$ 70,811
Internally Assigned Grade 5
Credit Quality Of Finance Receivables
Number of tenants | tenant	1	1
Net investments in direct financing leases	$ 1,733	$ 1,644