Description of Business and Basis of Presentation (Details Textual) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014 sqft	Dec. 31, 2013
Organization Consolidation And Presentation of Financial Statements
Company's portfolio of real estate assets - Office space (square feet)	15,679,000
Company's portfolio of real estate assets - Retail space (square feet)	80,000
Company's portfolio of real estate assets - apartment space (square feet)	404,000
Total Assets	$ 2,667,330	$ 2,273,206
Callaway [Member]
Organization Consolidation And Presentation of Financial Statements
Total Assets	2,100	4,600
Section 1031 Exchange VIE [Member]
Organization Consolidation And Presentation of Financial Statements
Total Assets	$ 353,200