Investment in Unconsolidated Joint Ventures Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 sqft	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Area of real estate property (in square feet)	3,073,000
Property occupied percentage	83.30%
Equity method investments	$ 135,784	$ 151,162
Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	40.00%
Area of real estate property (in square feet)	2,433,000
Property occupied percentage	82.70%
Equity method investments	77,412	93,171
US Airways Building
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	74.58%
Area of real estate property (in square feet)	225,000
Property occupied percentage	100.00%
Equity method investments	42,811	42,501
7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage in equity investments (in percent)	40.00%
Area of real estate property (in square feet)	415,000
Property occupied percentage	77.90%
Equity method investments	$ 15,561	$ 15,490
Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	7
Unconsolidated Properties | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	5
Unconsolidated Properties | US Airways Building
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	1
Unconsolidated Properties | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	1