Notes Receivable - Interest Income and Payments Received (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 1,854	$ 2,970	$ 4,225	$ 5,878
Payment received relating to notes receivables				10,446
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1,700	$ 2,600	3,200	5,100
Payment received relating to notes receivables			2,900	$ 3,000
Bonds A and B Series [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 40,700		$ 40,700		$ 38,200