Net Investment in Direct Financing Leases - Internal Ratings for Net Investment in DFLs (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	$ 714,352	$ 752,589
Percentage of DFL Portfolio	100.00%
Senior housing triple-net
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	$ 629,748
Percentage of DFL Portfolio	88.00%
Other non-reportable segments
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	$ 84,604
Percentage of DFL Portfolio	12.00%
Performing Loans
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	$ 358,490
Performing Loans | Senior housing triple-net
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	273,886
Performing Loans | Other non-reportable segments
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	84,604
Watch List Loans
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	355,862
Watch List Loans | Senior housing triple-net
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	355,862
Watch List Loans | Other non-reportable segments
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	0
Workout DFLs
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	0
Workout DFLs | Senior housing triple-net
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	0
Workout DFLs | Other non-reportable segments
Financing Receivable, Recorded Investment [Line Items]
Net investment in direct financing leases	$ 0