Investment in Unconsolidated Joint Ventures Income Statement of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Schedule of Equity Method Investments [Line Items]
Operating expenses	$ 94,161	$ 62,373
Net operating income	9,952	5,792
Interest Expense	15,244	10,329
Depreciation and amortization	40,280	27,945
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Revenues	16,338
Operating expenses	6,441
Net operating income	9,897
Interest Expense	5,188
Depreciation and amortization	7,251
Net income (loss)	(2,542)
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Revenues	1,126
Operating expenses	0
Net operating income	1,126
Interest Expense	104
Depreciation and amortization	522
Net income (loss)	500
Equity Method Investee | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Revenues	1,848
Operating expenses	850
Net operating income	998
Interest Expense	(85)
Depreciation and amortization	1,160
Net income (loss)	(77)
Equity Method Investee | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Revenues	13,364
Operating expenses	5,591
Net operating income	7,773
Interest Expense	5,169
Depreciation and amortization	5,569
Net income (loss)	$ (2,965)