Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Jul. 06, 2016
Jan. 06, 2016
Significant Accounting Policies [Line Items]                
Capitalized development and construction salaries and other related costs $ 800,000   $ 1,200,000 $ 1,300,000 $ 2,500,000      
Construction, tenant improvement, and development in-progress 226,700,000 $ 88,700,000   $ 226,700,000   $ 88,700,000    
Maximum period after cessation of major construction activity that projects are considered complete       1 year        
Threshold of investment value for discontinuation of equity method accounting 0     $ 0        
Amortization of deferred financing costs 1,180,000   948,000 2,349,000 1,901,000      
Gain from extinguishment of debt 12,420,000     12,420,000        
Write off of unamortized deferred financing costs       0 0      
Deferred leasing costs 870,000   846,000 1,650,000 1,816,000      
Deferred tax asset $ 23,000,000     23,000,000        
Income taxes, material adjustment amount       $ 0        
Common stock, shares outstanding 89,650,590 89,583,950   89,650,590   89,583,950   89,584,008
Common units outstanding 10,497,946 10,516,844   10,497,946   10,516,844   10,516,844
LTIP units outstanding 657,373     657,373        
Distributions payable, record date       Jul. 06, 2016   Jan. 06, 2016    
Distributions payable, approved date   Dec. 08, 2015   Jun. 01, 2016        
Common stock dividends and common unit distributions per share   $ 0.15   $ 0.15        
Restricted stock expense $ 1,469,000   $ 492,000 $ 2,253,000 $ 805,000      
Distributions payable, pay date   Jan. 15, 2016   Jul. 15, 2016        
Subsequent Event [Member]                
Significant Accounting Policies [Line Items]                
Common stock, shares outstanding             89,650,641  
Common units outstanding             10,497,946  
LTIP units outstanding             657,373