Mortgage Notes Receivable - Aggregate Principal Payments (Details) - Mortgage notes receivable [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Due within one year	$ 930
Due after one year through five years	4,422
Due after five years through 10 years	7,089
Due after 10 years	13,837
Total	26,278
Interest scheduled to be capitalized	$ 3,800