Investment in Unconsolidated Joint Ventures - Balance Sheet of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Real estate, net	$ 2,566,463	$ 2,316,795
Total assets	3,268,456	2,925,501
Mortgage debt	1,107,628	1,097,493
Total liabilities and partners' equity	3,268,456	2,925,501
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Cash	13,633	12,082
Restricted cash	403	5,846
Real estate, net	807,868	822,591
Intangible assets, net	64,594	63,234
Other assets	23,053	21,930
Total assets	909,551	925,683
Mortgage debt	671,108	671,843
Other liabilities	50,564	58,382
Partners' equity	187,879	195,458
Total liabilities and partners' equity	909,551	925,683
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Cash	148	2,471
Restricted cash	0	0
Real estate, net	48,018	49,176
Intangible assets, net	5,214	2,809
Other assets	710	3,145
Total assets	54,090	57,601
Mortgage debt	13,525	13,777
Other liabilities	372	1,143
Partners' equity	40,193	42,681
Total liabilities and partners' equity	54,090	57,601
Equity Method Investee | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Cash	522	179
Restricted cash	200	0
Real estate, net	48,659	49,852
Intangible assets, net	5,262	4,832
Other assets	1,464	4,147
Total assets	56,107	59,010
Mortgage debt	30,000	30,000
Other liabilities	1,161	1,687
Partners' equity	24,946	27,323
Total liabilities and partners' equity	56,107	59,010
Equity Method Investee | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Cash	12,963	9,432
Restricted cash	203	5,846
Real estate, net	711,191	723,563
Intangible assets, net	54,118	55,593
Other assets	20,879	14,638
Total assets	799,354	809,072
Mortgage debt	627,583	628,066
Other liabilities	49,031	55,552
Partners' equity	122,740	125,454
Total liabilities and partners' equity	$ 799,354	$ 809,072