Investment in Unconsolidated Joint Ventures - Balance Sheet of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Real estate, net	$ 3,100,478	$ 3,024,271
Total assets	3,756,697	3,704,714
Mortgage debt	1,298,971	1,339,450
Total liabilities and partners' equity	3,756,697	3,704,714
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Cash	433	1,364
Restricted cash	251	269
Real estate, net	95,674	96,164
Intangible assets, net	8,704	9,235
Other assets	3,298	2,923
Total assets	108,360	109,955
Mortgage debt	43,357	43,441
Other liabilities	2,014	1,931
Partners' equity	62,989	64,583
Total liabilities and partners' equity	108,360	109,955
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Cash	146	146
Restricted cash	0	0
Real estate, net	47,245	47,632
Intangible assets, net	4,942	5,078
Other assets	937	824
Total assets	53,270	53,680
Mortgage debt	13,357	13,441
Other liabilities	371	370
Partners' equity	39,542	39,869
Total liabilities and partners' equity	53,270	53,680
Equity Method Investee | 7000 Central Park JV LLC
Schedule of Equity Method Investments [Line Items]
Cash	287	1,218
Restricted cash	251	269
Real estate, net	48,429	48,532
Intangible assets, net	3,762	4,157
Other assets	2,361	2,099
Total assets	55,090	56,275
Mortgage debt	30,000	30,000
Other liabilities	1,643	1,561
Partners' equity	23,447	24,714
Total liabilities and partners' equity	$ 55,090	$ 56,275