Investment in Unconsolidated Joint Ventures - Income Statement of Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Revenues	$ 112,551	$ 114,843	$ 126,905	$ 119,684	$ 126,381	$ 115,747	$ 110,460	$ 104,113	$ 473,983	$ 456,701	$ 291,579
Operating expenses	(98,788)	(101,717)	(115,439)	(107,407)	(133,253)	(106,275)	(103,390)	(94,160)	(423,351)	(437,078)	(285,091)
Depreciation and amortization									(190,387)	(182,955)	(118,031)
Operating income	13,763	13,126	11,466	12,277	(6,872)	9,472	7,070	9,953	50,632	19,623	6,488
Net gains on sale of real estate	3,819	47,351	45,246	14,316	69,714	6,664	0	0	110,732	76,378	0
Loss on extinguishment of debt	(520)	(702)	(4,919)	79	(2,066)	0	(339)	0	(6,062)	(2,405)	0
Interest expense	$ (17,590)	$ (17,017)	$ (17,676)	$ (19,198)	$ (17,515)	$ (16,543)	$ (16,793)	$ (15,244)	(71,481)	(66,095)	(45,622)
Loan cost amortization									(3,112)	(2,845)	$ (2,448)
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Revenues									4,504	4,504
Operating expenses									(8)	(3)
Depreciation and amortization									(2,089)	(2,089)
Operating income									2,407	2,412
Net gains on sale of real estate									0
Loss on extinguishment of debt									0
Interest expense									(404)	(413)
Loan cost amortization									0	0
Other expenses										0
Net income									2,003	1,999
Equity Method Investee | 7000 Central Park
Schedule of Equity Method Investments [Line Items]
Revenues									6,840	7,430
Operating expenses									(3,376)	(3,856)
Depreciation and amortization									(3,911)	(4,352)
Operating income									(447)	(778)
Net gains on sale of real estate									30,478
Loss on extinguishment of debt									(172)
Interest expense									(533)	(593)
Loan cost amortization									(720)	(176)
Other expenses										0
Net income									$ 28,606	(1,547)
Equity Method Investee | PKY CalSTRS Austin, LLC
Schedule of Equity Method Investments [Line Items]
Revenues										86,548
Operating expenses										(36,467)
Depreciation and amortization										(32,877)
Operating income										17,204
Interest expense										(33,671)
Loan cost amortization										565
Other expenses										(1)
Net income										$ (15,903)