Notes Receivable - Interest Income and Payments Received (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 1,540	$ 2,878	$ 5,765	$ 8,756
Payment received relating to notes receivables			2,985	13,211
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1,500	$ 2,500	4,700	7,700
Payment received relating to notes receivables			8,800	$ 11,300
Bonds A and B Series [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 39,400		$ 39,400		$ 38,200