Investment in Unconsolidated Joint Ventures (Narrative) (Details)	6 Months Ended
	Jun. 30, 2017 property joint_venture
Schedule of Equity Method Investments [Line Items]
Number of properties | property	145
2001 Sixth Avenue, 2020 Fifth Avenue, 33 Chun Choi Street
Schedule of Equity Method Investments [Line Items]
Number of joint ventures | joint_venture	3
2001 Sixth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	50.00%
2020 Fifth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	50.00%
33 Chun Choi Street Hong Kong
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	50.00%
Prudential Real Estate Investors and Griffin Capital Essential Asset REIT, Inc.
Schedule of Equity Method Investments [Line Items]
Number of joint ventures | joint_venture	2
PREI
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	20.00%
Number of joint ventures | joint_venture	1
Number of properties | property	10
GCEAR
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	20.00%
Number of properties | property	1
1101 Space Park Drive
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	17.00%