Investment in Mortgage Notes (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018	Jan. 02, 2018 properties	Apr. 06, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 517,467	$ 970,749
Mortgage notes and related accrued interest receivable, net		515,811
Number of properties securing debt | properties						1
Proceeds from mortgage note receivable paydown		$ 335,168	21,784	$ 72,072
Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties securing debt							14
Mortgage Receivable [Member] | Corporation [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties securing debt		4
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, Converted under ASC 610-20, Bridgeton, NJ [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[1]	$ 0	2,500
Mortgage Loans on Real Estate, Interest Rate		10.14%
Mortgage notes and related accrued interest receivable, net	[1]	$ 0
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, Converted under ASC 610-20, Evans, Georgia [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[1]	$ 0	9,631
Mortgage Loans on Real Estate, Interest Rate		8.50%
Mortgage notes and related accrued interest receivable, net	[1]	$ 0
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, Converted to lease [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[2]	$ 0	142,900
Mortgage Loans on Real Estate, Interest Rate		7.25%
Mortgage notes and related accrued interest receivable, net	[2]	$ 0
Number of properties securing debt		28
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, paid in full March 11, 2018 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[3]	$ 0	1,474
Mortgage Loans on Real Estate, Interest Rate		7.00%
Mortgage notes and related accrued interest receivable, net	[3]	$ 0
Number of properties securing debt		1
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		$ 0
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, paid in full March 26, 2018 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[4]	$ 0	9,056
Mortgage Loans on Real Estate, Interest Rate		7.50%
Mortgage notes and related accrued interest receivable, net	[4]	$ 0
Number of properties securing debt		1			1
Proceeds from mortgage note receivable paydown		$ 9,000
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		0
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 8.50%, paid in full September 27, 2018 | Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[5]	$ 0	249,213
Mortgage Loans on Real Estate, Interest Rate		8.50%
Mortgage notes and related accrued interest receivable, net	[5]	$ 0
Number of properties securing debt		14
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		$ 65,900
Mortgage Loans on Real Estate, Collections of Principal		250,300
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, paid in full November 30, 2018 | Montparnasse56 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[6]	$ 0	31,105
Mortgage Loans on Real Estate, Interest Rate		9.25%
Mortgage notes and related accrued interest receivable, net	[6]	$ 0
Number of properties securing debt		1
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		$ 5,400
Mortgage Loans on Real Estate, Collections of Principal		32,000
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, Paid in full December 11, 2018 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[7]	$ 0	5,173
Mortgage Loans on Real Estate, Interest Rate		9.00%
Mortgage notes and related accrued interest receivable, net	[7]	$ 0
Number of properties securing debt		1
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		$ 3,400
Mortgage Loans on Real Estate, Collections of Principal		0
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, three properties, Paid in full December 11, 2018 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[7]	$ 0	33,269
Mortgage Loans on Real Estate, Interest Rate		10.00%
Mortgage notes and related accrued interest receivable, net	[7]	$ 0
Number of properties securing debt		3
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, Paid in full December 21, 2018 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net	[8]	$ 0	1,454
Mortgage Loans on Real Estate, Interest Rate		9.00%
Mortgage notes and related accrued interest receivable, net	[8]	$ 0
Number of properties securing debt		1
Proceeds from Maturities, Prepayments and Calls of Securities, Operating Activities		$ 0
Mortgage Loans on Real Estate, Collections of Principal		1,400
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, Due May 1, 2019 | Water Parks [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		179,846	174,265
Mortgage notes and related accrued interest receivable, net		$ 179,846
Number of properties securing debt		3
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 7.00% due December 20, 2021 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 54,535	57,890
Mortgage Loans on Real Estate, Interest Rate		7.00%
Mortgage notes and related accrued interest receivable, net		$ 54,535
Number of properties securing debt		8
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 7.85%, due December 28, 2018 | fitness center [Member] [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 5,803	5,803
Mortgage Loans on Real Estate, Interest Rate		7.85%
Mortgage notes and related accrued interest receivable, net		$ 5,766
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 7.85%, due January 3, 2027 [Member] | Other Recreation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 10,977	10,880
Mortgage Loans on Real Estate, Interest Rate		7.85%
Mortgage notes and related accrued interest receivable, net		$ 10,905
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, 11.31%, due July 1, 2033 | TopGolf [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 11,934	12,249
Mortgage Loans on Real Estate, Interest Rate		11.31%
Mortgage notes and related accrued interest receivable, net		$ 11,934
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, due June 30, 2034 | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 8,835	8,711
Mortgage notes and related accrued interest receivable, net		$ 8,595
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, 10.00%, due August 31, 2034 | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 15,652	12,564
Mortgage Loans on Real Estate, Interest Rate		10.00%
Mortgage notes and related accrued interest receivable, net		$ 15,239
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 11.43%, due December 1, 2034 | Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 51,050	51,050
Mortgage Loans on Real Estate, Interest Rate		11.43%
Mortgage notes and related accrued interest receivable, net		$ 51,050
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, 10.59%, due December 1, 2034 | Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 37,562	37,562
Mortgage Loans on Real Estate, Interest Rate		10.59%
Mortgage notes and related accrued interest receivable, net		$ 37,562
Number of properties securing debt		4
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 11.04%, due December 1, 2034 [Member] | Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 4,550	4,550
Mortgage Loans on Real Estate, Interest Rate		11.04%
Mortgage notes and related accrued interest receivable, net		$ 4,550
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 8.28%, due January 5, 2036 | Ski Resorts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 21,000	21,000
Mortgage Loans on Real Estate, Interest Rate		8.28%
Mortgage notes and related accrued interest receivable, net		$ 21,000
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, due May 31, 2036 | TopGolf [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 17,505	17,505
Mortgage Loans on Real Estate, Interest Rate		10.25%
Mortgage notes and related accrued interest receivable, net		$ 17,505
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 10.14% due July 31 2036 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 6,383	6,304
Mortgage Loans on Real Estate, Interest Rate		10.14%
Mortgage notes and related accrued interest receivable, net		$ 6,224
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 9.75% due August 1, 2036 | TopGolf [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 18,068	18,068
Mortgage Loans on Real Estate, Interest Rate		9.75%
Mortgage notes and related accrued interest receivable, net		$ 18,068
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 9.95% due December 31, 2036 | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 9,839	9,838
Mortgage Loans on Real Estate, Interest Rate		9.95%
Mortgage notes and related accrued interest receivable, net		$ 9,765
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 8.67%, due April 30, 2037 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 4,952	4,717
Mortgage Loans on Real Estate, Interest Rate		8.67%
Mortgage notes and related accrued interest receivable, net		$ 4,674
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 8.93%, due July 30, 2037 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 4,165	4,111
Mortgage Loans on Real Estate, Interest Rate		8.93%
Mortgage notes and related accrued interest receivable, net		$ 4,121
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 8.67%, due July 30, 2037 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 4,236	4,235
Mortgage Loans on Real Estate, Interest Rate		8.67%
Mortgage notes and related accrued interest receivable, net		$ 4,206
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 8.75%, due August 31, 2037 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 23,718	11,330
Mortgage Loans on Real Estate, Interest Rate		8.75%
Mortgage notes and related accrued interest receivable, net		$ 23,718
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 9.02%, due September 30, 2037 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 14,325	11,684
Mortgage Loans on Real Estate, Interest Rate		9.02%
Mortgage notes and related accrued interest receivable, net		$ 14,084
Number of properties securing debt		1
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Note, 7.85% due January 31, 2038 [Member] | fitness center [Member] [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 10,360	0
Mortgage Loans on Real Estate, Interest Rate		7.85%
Mortgage notes and related accrued interest receivable, net		$ 10,292
Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, 7.50, due August 30, 2038 [Member] | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Notes and Related Accrued Interest Receivable, Net		$ 2,172	$ 658
Mortgage Loans on Real Estate, Interest Rate		7.50%
Mortgage notes and related accrued interest receivable, net		$ 2,172
Minimum [Member] | Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, Due May 1, 2019 | Water Parks [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Interest Rate		7.00%
Minimum [Member] | Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, due June 30, 2034 | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Interest Rate		8.71%
Maximum [Member] | Mortgage Receivable [Member] | Corporation [Member] | Mortgage Notes, Due May 1, 2019 | Water Parks [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Interest Rate		10.00%
Maximum [Member] | Mortgage Receivable [Member] | Corporation [Member] | Mortgage note, due June 30, 2034 | Education Property [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans on Real Estate, Interest Rate		9.38%
Education Reportable Operating Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from Conversion of Mortgage Note		142,900,000
Number of Properties Securing Mortgage Note Converted to Rental Properties		28
Education Reportable Operating Segment [Member] | early childhood education center [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from mortgage note receivable paydown		$ 1,500

[1] Mortgage note was reclassified to rental properties on January 1, 2018, due to implementation of ASC 610-20.

[2] On February 16, 2018, the borrower exercised its put option to convert its mortgage note agreement, totaling $142.9 million and secured by 28 education facilities, including both early education and private school properties, to a lease agreement. As a result, the Company recorded the rental property at the carrying value, which approximated fair value of the mortgage note on the conversion date, and allocated this cost on a relative fair value basis.

[3] On March 11, 2018, the Company received payment in full on one mortgage note receivable of $1.5 million that was secured by land located in California. There was no prepayment fee received in connection with this note payoff.

[4] On March 26, 2018, the Company received payment in full on one mortgage note receivable of $9.0 million that was secured by real estate in Washington. There was no prepayment fee received in connection with this note payoff.

[5] During the year ended December 31, 2018, the Company received payment in full on the mortgage note receivable of $250.3 million from OZRE that was secured by 14 ski properties. In connection with the prepayment of this note, the Company recognized prepayment fees totaling $65.9 million that are included in mortgage and other financing income in the accompanying consolidated statements of income for the year ended December 31, 2018.

[6] During the year ended December 31, 2018, the Company received payment in full on the mortgage note receivable of $32.0 million that was secured by the observation deck of the John Hancock Tower in Chicago, Illinois. In connection with the prepayment of this note, the Company recognized prepayment fees of $5.4 million that are included in mortgage and other financing income in the accompanying consolidated statements of income for the year ended December 31, 2018.

[7] On December 11, 2018, the Company received payment in full on the mortgage notes receivable totaling $36.7 million from LBE Investments, Ltd. that were secured by four charter school properties located in Gilbert and Queen Creek, Arizona. In connection with the prepayment of these notes, the Company recognized prepayment fees totaling $3.4 million that are included in mortgage and other financing income in the accompanying consolidated statements of income for the year ended December 31, 2018.

[8] On December 21, 2018, the Company received payment in full on a mortgage note receivable of $1.4 million from LBE Investments, Ltd. that was secured by land located in Queen Creek, Arizona. No prepayment fee was received in connection with the prepayment of this note.