Notes Receivable - Interest Income and Payment Received (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 1,370	$ 2,371
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	1,300	1,500
Payment received relating to notes receivables	2,800	$ 2,900
Bonds A and B Series [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 39,500		$ 40,900