Fair Value Measurements - Impairment of Assets Measured on a Non-Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impairment Disclosure
Impairment charges on properties	$ 52,300
Impairment Charges in Continuing Operations
Impairment Disclosure
Impairment charges on properties	59,303	$ 29,906	$ 23,802
Impairment Charges in Continuing Operations | Real Estate
Impairment Disclosure
Total fair value measurements	155,839	63,027	26,503
Impairment charges on properties	52,316	26,597	21,738
Impairment Charges in Continuing Operations | Net investments in direct financing lease
Impairment Disclosure
Total fair value measurements	23,775	65,132	39,158
Impairment charges on properties	6,987	3,309	1,329
Impairment Charges in Continuing Operations | Equity investments in real estate
Impairment Disclosure
Total fair value measurements	0	0	0
Impairment charges on properties	$ 0	$ 0	$ 735