Investments In Direct Financing Leases (Narrative) (Details)			9 Months Ended	12 Months Ended
	May 22, 2015 properties	Apr. 02, 2014 properties	Sep. 30, 2014 USD ($)	Dec. 31, 2016 USD ($) properties years	Dec. 31, 2015 USD ($) properties	Dec. 31, 2014 USD ($)	Nov. 02, 2016 properties	Feb. 18, 2016 properties	May 21, 2015 USD ($)	Apr. 03, 2014 USD ($)
Initial direct costs				$ 1,300,000	$ 1,400,000
Allowance for lease losses				0	0
Investment in a direct financing lease, net				102,698,000	190,880,000				$ 4,700,000	$ 45,900,000
Proceeds from Sale of Lease Receivables				20,951,000	4,741,000	$ 46,092,000
Mortgage notes and related accrued interest receivable, net				$ 613,978,000	423,780,000
number of properties sold | properties	1	4		9
Gain (Loss) on Contract Termination					0
Net Investment in Direct Financing and Sales Type Leases, Carrying Value of Investments Sold				$ 91,300,000
Gain (Loss) on Disposition of Property Plant Equipment			$ 200,000	$ 0	$ 0
Number of properties securing debt | properties				11			14	1
Maximum [Member]
Length of lease (in years) | years				18
Minimum [Member]
Length of lease (in years) | years				15
Imagine Schools [Member]
Number of public charter school properties | properties				12	21
Mortgage notes and related accrued interest receivable, net				$ 70,300,000
number of properties sold | properties				7
Third Parties [Member]
number of properties sold | properties				2