Investment in Unconsolidated Joint Ventures - Income Statement of Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Operating expenses		$ 115,439	$ 103,389	$ 222,846	$ 197,549
Depreciation and amortization				96,192	85,261
Operating income		11,466	7,070	23,743	17,023
Interest expense		17,676	17,132	36,874	32,377
Loan cost amortization				1,624	1,740
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Revenues		3,167	27,482	6,134	54,599
Operating expenses		949	10,830	1,983	21,537
Depreciation and amortization		1,664	10,917	3,815	22,501
Operating income		554	5,735	336	10,561
Interest expense		251	9,830	500	19,334
Loan cost amortization		41	(104)	84	(216)
Other Expenses			1		1
Net income (loss)		262	(3,992)	(248)	(8,558)
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Revenues		1,126	1,126	2,252	2,252
Operating expenses		0	0	0	0
Depreciation and amortization		522	522	1,044	1,044
Operating income		604	604	1,208	1,208
Interest expense		101	103	202	207
Loan cost amortization		0	0	0	0
Other Expenses			0		0
Net income (loss)		503	501	1,006	1,001
Equity Method Investee | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Revenues		2,041	1,921	3,882	3,769
Operating expenses		949	1,023	1,983	1,873
Depreciation and amortization		1,142	1,181	2,771	2,293
Operating income		(50)	(283)	(872)	(397)
Interest expense		150	148	298	63
Loan cost amortization		41	57	84	106
Other Expenses			0		0
Net income (loss)		(241)	(488)	(1,254)	(566)
Equity Method Investee | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Revenues	[1]	0	24,435	0	48,578
Operating expenses	[1]	0	9,807	0	19,664
Depreciation and amortization	[1]	0	9,214	0	19,164
Operating income	[1]	0	5,414	0	9,750
Interest expense	[1]	0	9,579	0	19,064
Loan cost amortization	[1]	0	(161)	0	(322)
Other Expenses	[1]		1		1
Net income (loss)	[1]	$ 0	$ (4,005)	$ 0	$ (8,993)

[1] The Company previously owned an indirect interest in PKY/CalSTRS Austin, LLC (the "Austin Joint Venture"), a joint venture with the California State Teachers' Retirement System ("CalSTRS"). The Company terminated the Austin Joint Venture on November 17, 2014.