Investment in Unconsolidated Joint Venture (Condensed Income Statement) (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]
Rental income	$ 32,130	$ 26,104	$ 64,661	$ 53,275
Other revenue	4,184	3,303	8,346	6,819
Total revenues	43,677	35,949	84,579	69,541
Property operating	10,098	8,304	21,067	17,162
Depreciation and amortization	22,154	20,222	42,886	41,235
Total operating expenses	47,147	100,510	91,737	136,958
Operating income	(3,470)	(64,561)	(7,158)	(67,417)
Interest expense	(6,024)	(4,813)	(11,957)	(8,752)
Net loss	(8,916)	(67,748)	(17,376)	(75,903)
Net loss attributable to stockholders	(8,659)	(67,237)	(16,858)	(75,393)
Company's share of net loss from Worldwide Plaza			805	(1,036)
Income (loss) from unconsolidated joint venture	570	948	805	(1,036)
Worldwide Plaza
Schedule of Equity Method Investments [Line Items]
Rental income	30,751	27,739	61,265	55,394
Other revenue	1,232	1,229	2,449	2,444
Total revenues	31,983	28,968	63,714	57,838
Property operating	11,727	10,779	23,967	22,292
Depreciation and amortization	6,864	6,260	13,714	12,628
Total operating expenses	18,591	17,039	37,681	34,920
Operating income	13,392	11,929	26,033	22,918
Interest expense	(9,992)	(9,992)	(19,874)	(19,874)
Net loss	3,400	1,937	6,159	3,044
Preferred return	(3,894)	(1,334)	(7,745)	(7,745)
Net loss attributable to stockholders	(494)	603	(1,586)	(4,701)
Company's preferred return	3,894	3,894	7,745	7,745
Company's share of net loss from Worldwide Plaza	(242)	(957)	(776)	(2,299)
Amortization of basis difference	(3,082)	(3,241)	(6,164)	(6,482)
Reallocation of net loss to members	$ 0	$ 1,252	$ 0	$ 0