Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies (Narrative) (Details)

v3.8.0.1
Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Oct. 03, 2017
Jan. 05, 2017
Significant Accounting Policies [Line Items]                
Capitalized development and construction salaries and other related costs $ 600,000   $ 700,000 $ 1,800,000 $ 1,900,000      
Construction, tenant improvement, and development in-progress 466,800,000 $ 361,100,000   $ 466,800,000   $ 361,100,000    
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 1,184,000   1,234,000 3,462,000 3,583,000      
Loss from extinguishment of debt, net       (239,000) 12,420,000      
Write off of unamortized deferred financing costs 0   346,000 239,000 346,000      
Deferred leasing costs 607,000   790,000 2,595,000 2,440,000      
Deferred tax asset $ 17,100,000     17,100,000        
Income taxes, material adjustment amount       $ 0        
Common stock, shares outstanding 89,913,576 89,696,713   89,913,576   89,696,713   89,696,824
Common units outstanding 10,438,855 10,488,105   10,438,855   10,488,105   10,488,105
LTIP units outstanding 1,230,877 657,373   1,230,877   657,373   657,373
Distributions payable, record date       Oct. 03, 2017   Jan. 05, 2017    
Distributions payable, approved date   Dec. 13, 2016   Sep. 14, 2017        
Common stock dividends and common unit distributions per share   $ 0.15   $ 0.20        
Restricted stock expense $ 2,169,000   $ 2,046,000 $ 5,268,000 $ 4,299,000      
Distributions payable, pay date   Jan. 13, 2017   Oct. 13, 2017        
Subsequent Event [Member]                
Significant Accounting Policies [Line Items]                
Common stock, shares outstanding             89,913,684  
Common units outstanding             10,438,855  
LTIP units outstanding             1,230,877