Other Commitments And Contingencies (Details)		1 Months Ended								9 Months Ended		12 Months Ended
	Oct. 20, 2011 USD ($) claim	Oct. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) properties mortgagenotes developmentproject	Aug. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) properties mortgagenotes developmentproject	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) properties	Dec. 31, 2016 USD ($)
Litigation Settlement, Expense										$ 90,000
Loss Contingency, Claims Settled and Dismissed, Number | claim	2
Commitment to fund project development			$ 84,400,000							$ 84,400,000
Number of Surety Bonds			5							5
Surety bonds			$ 22,500,000							$ 22,500,000
Number of Mortgage Notes Receivable (in mortgage notes) | mortgagenotes			4							4
Mortgage notes receivable with commitments										$ 11,700,000
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 24,700,000							24,700,000
Loss Contingency, Damages Sought, Value	$ 800,000,000
Litigation Settlement, Amount Awarded to Other Party										2,000,000
Loss Contingency, New Claims Filed, Number | claim	3
Tenant Reimbursements										$ 11,400,000	$ 11,400,000
Theatre Properties [Member]
Development projects in process (in projects) | developmentproject			11							11
Commitment to fund project development			$ 20,100,000							$ 20,100,000
recreationproperties [Member]
Development projects in process (in projects) | developmentproject			5							5
Commitment to fund project development			$ 51,100,000							$ 51,100,000
Concord Resort [Member]
Commitment to fund project development			203,700,000							203,700,000
Adelaar Infrastructure [Member]
Special Assessment Bond			$ 110,000,000							110,000,000
Property under development										$ 6,900,000		$ 23,900,000	$ 43,400,000
Education Property Member
Development projects in process (in projects) | developmentproject			4							4
Commitment to fund project development			$ 13,200,000							$ 13,200,000
Louisiana Theatre Properties [Member]
Economic Development Revenue Bond Term										30 years
Development projects in process (in projects) | developmentproject			2							2
Economic development revenue bond annual fees percentage										4.00%
Deferred assets related to guarantee			$ 13,300,000							$ 13,300,000
Deferred liabilities related to guarantee			13,300,000							13,300,000
Loss contingency										0
Waterpark Hotel and Adventure Park [Member] | Kiamesha Lake NY [Member]
Commitment to fund project development			$ 129,500,000							$ 129,500,000
Children's Learning Adventure USA, LLC [Member]
Subsidiaries filing for bankruptcy | properties												10
Bankruptcy Claims, Number Claims Filed | properties												24
Number of Real Estate Properties | properties			25							25
Property Subject to or Available for Operating Lease, Number of Units | properties			21							21
Payments for Rent			$ 1,000,000	$ 1,000,000	$ 1,000,000	$ 1,000,000	$ 750,000	$ 750,000	$ 750,000
Tenant Reimbursements			$ 170,000
Children's Learning Adventure USA, LLC [Member] | land held for development [Member]
number of properties under construction | properties												2
number of properties in land held for development | properties			4							4		1
Subsequent Event [Member] | Children's Learning Adventure USA, LLC [Member]
Payments for Rent		$ 1,000,000