Segment Reporting Narrative (Details) ft² in Thousands	9 Months Ended
	Sep. 30, 2017 ft² building	May 02, 2016
Segment Reporting Information [Line Items]
Rentable aggregate square feet	1,000
Number of buildings | building	4
Number of buildings with one tenant | building	2
One Tenant Lease
Segment Reporting Information [Line Items]
Rentable aggregate square feet	660
Lease term	20 years
Subsidiary Lease
Segment Reporting Information [Line Items]
Rentable aggregate square feet	135
Lease term	130 months
Great Park Venture
Segment Reporting Information [Line Items]
Percentage of equity ownership	37.50%	37.50%
Gateway Commercial Venture
Segment Reporting Information [Line Items]
Percentage of equity ownership	75.00%