Investment in Unconsolidated Joint Ventures - Unconsolidated Joint Ventures (Details) (Unconsolidated Properties, USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 Property		Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	7
Equity method investments	$ 130,511		$ 151,162
Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	40.00%	[1]
Number of real estate properties	5	[1]
Equity method investments	74,843	[1]	93,171	[1]
US Airways Building
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	74.58%
Number of real estate properties	1
Equity method investments	40,065		42,501
7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	40.00%
Number of real estate properties	1
Equity method investments	$ 15,603		$ 15,490

[1] The Austin Joint Venture owns the following properties: San Jacinto Center; Frost Bank Tower; One Congress Plaza; One American Center; and 300 West 6th Street.