Notes Receivable - Interest Income and Payments Received (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 2,970	$ 2,766	$ 5,878	$ 5,519
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 2,600	$ 2,700	5,100	5,300
Payment received relating to notes receivables			$ 3,000	$ 3,100