Other Assets - Unconsolidated Joint Ventures (Details)	3 Months Ended			12 Months Ended
	Dec. 31, 2017 building	Dec. 31, 2017 USD ($)	Dec. 31, 2017 Garage	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Equity Method Investments [Roll Forward]
Net LLC investments, beginning of period				$ 8,700,000
Equity income (loss) recognized during the period				4,000	$ 7,000
Owner distributions				(200,000)	0
Net LLC investments, end of period		$ 8,700,000		8,500,000	8,700,000
Parking Garages [Member]
Property, Plant and Equipment [Line Items]
Number of parking garages	2		2
Number of buildings acquired | building	3
Equity Method Investments [Roll Forward]
Net LLC investments, beginning of period				8,700,000	0
New investments during the period		8,700,000		0	8,700,000
Equity income (loss) recognized during the period				0	0
Net LLC investments, end of period		$ 8,700,000		$ 8,500,000	$ 8,700,000