Notes Receivable - Interest Income and Payments Received (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 10,469	$ 11,818	$ 11,500
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	10,100	11,600	11,400
Payment received relating to notes receivables	$ 10,900	$ 11,100	$ 11,100