Investment in Unconsolidated Joint Ventures - Income Statement of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Equity Method Investments [Line Items]
Operating expenses	$ 103,389	$ 67,047	$ 197,549	$ 129,420
Depreciation and amortization			85,261	57,776
Operating income (loss)	7,070	5,576	17,023	11,368
Interest expense	17,132	11,162	32,377	21,491
Amortization of debt premium, net			(2,678)	0
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Revenues	27,482	299	54,599	299
Operating expenses	10,830	0	21,537	0
Depreciation and amortization	10,917	193	22,501	193
Operating income (loss)	5,735	106	10,561	106
Interest expense	9,830	0	19,334	0
Amortization of debt premium, net	(104)	0	(216)	0
Other expenses	1	0	1	0
Net income (loss)	(3,992)	106	(8,558)	106
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Revenues	1,126	299	2,252	299
Operating expenses	0	0	0	0
Depreciation and amortization	522	193	1,044	193
Operating income (loss)	604	106	1,208	106
Interest expense	103	0	207	0
Amortization of debt premium, net	0	0	0	0
Other expenses	0	0	0	0
Net income (loss)	501	106	1,001	106
Equity Method Investee | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Revenues	1,921	0	3,769	0
Operating expenses	1,023	0	1,873	0
Depreciation and amortization	1,181	0	2,293	0
Operating income (loss)	(283)	0	(397)	0
Interest expense	148	0	63	0
Amortization of debt premium, net	57	0	106	0
Other expenses	0	0	0	0
Net income (loss)	(488)	0	(566)	0
Equity Method Investee | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Revenues	24,435	0	48,578	0
Operating expenses	9,807	0	19,664	0
Depreciation and amortization	9,214	0	19,164	0
Operating income (loss)	5,414	0	9,750	0
Interest expense	9,579	0	19,064	0
Amortization of debt premium, net	(161)	0	(322)	0
Other expenses	1	0	1	0
Net income (loss)	$ (4,005)	$ 0	$ (8,993)	$ 0