Fair Value Measurements - Narratives (Details) $ in Thousands	1 Months Ended				3 Months Ended			12 Months Ended
	May 31, 2017 property	Jan. 31, 2017 property	Dec. 31, 2016 USD ($) property	Oct. 31, 2016 USD ($) property	Dec. 31, 2017 USD ($) property	Sep. 30, 2017 property	Sep. 30, 2016 property	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($) property
Fair value inputs
Unamortized discount					$ 12,829			$ 12,829
Goodwill, impairment loss									$ 10,191
Number of properties disposed | property					5	5	4
Fair Value, Measurements, Nonrecurring | Level 3
Fair value inputs
Impairment charges on properties								2,769	59,303	$ 29,906
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles
Fair value inputs
Impairment charges on properties								$ 2,769	$ 52,316	$ 26,597
Number of real estate properties | property			18		2			2	18	7
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Impaired Properties
Fair value inputs
Impairment charges on properties								$ 600		$ 10,900
Number of properties disposed | property				1				2		2
Number of real estate properties | property										5
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Industrial facilities in Erlanger, KY
Fair value inputs
Impairment charges on properties										$ 8,700
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Industrial facilities in Erlanger, KY | Cash flows
Fair value inputs
Discount rate										9.25%
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Industrial facilities in Erlanger, KY | Residual discount rate
Fair value inputs
Discount rate										9.75%
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Industrial facilities in Erlanger, KY | Residual capitalization rates
Fair value inputs
Discount rate										8.50%
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Building
Fair value inputs
Impairment charges on properties				$ 6,900				$ 2,200
Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles | Noncontrolling interest
Fair value inputs
Impairment charges on properties									$ 1,200	$ 1,000
Fair Value, Measurements, Nonrecurring | Level 3 | Net investments in direct financing leases
Fair value inputs
Impairment charges on properties								0	$ 6,987	$ 3,309
Number of real estate properties | property			1						1	5
Impaired Portfolio | Fair Value, Measurements, Nonrecurring | Level 3
Fair value inputs
Impairment charges on properties									$ 41,000
Impaired Portfolio | Fair Value, Measurements, Nonrecurring | Level 3 | Land, buildings and improvements and intangibles
Fair value inputs
Impairment charges on properties									41,000
Goodwill, impairment loss									$ 10,200
Number of properties disposed | property	1	2	1						4
Number of real estate properties | property			14						14
Senior Unsecured Notes
Fair value inputs
Unamortized discount			$ 7,800		$ 9,900			9,900	$ 7,800
Carrying Value | Non-Recourse Debt | Level 3
Fair value inputs
Debt instrument, unamortized discount and debt issuance costs, net			1,300		1,000			1,000	1,300
Unamortized discount			200		1,700			1,700	200
Carrying Value | Senior Unsecured Notes | Level 2
Fair value inputs
Debt instrument, unamortized discount and debt issuance costs, net			12,100		14,700			14,700	12,100
Unamortized discount			$ 7,800		$ 9,900			$ 9,900	$ 7,800