Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 6 Months Ended 12 Months Ended
May. 11, 2015
Dec. 09, 2014
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Significant Accounting Policies [Line Items]              
Capitalized development and construction salaries and other related costs     $ 1,200,000 $ 900,000 $ 2,500,000 $ 1,800,000  
Construction, tenant improvement, and development in-progress     83,200,000   $ 83,200,000   $ 62,800,000
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     948,000 759,000 1,901,000 1,528,000  
Write off of unamortized deferred financing costs         0 0  
Deferred leasing costs     846,000 845,000 1,816,000 1,876,000  
Deferred tax asset     $ 15,300,000   15,300,000    
Income taxes, material adjustment amount         $ 0    
Common stock, shares outstanding 89,089,666 88,866,652 89,195,529   89,195,529   89,076,578
Common units outstanding 11,012,069 11,083,876 11,012,069   11,012,069   11,083,876
Distributions payable, record date         Jul. 06, 2015   Jan. 06, 2015
Distributions payable, approved date         May 11, 2015   Dec. 09, 2014
Common stock dividends and common unit distributions per share $ 0.15 $ 0.15          
Restricted stock expense     $ 492,000 877,000 $ 805,000 4,264,000  
Distributions payable, pay date         Jul. 14, 2015   Jan. 14, 2015
Difference between other comprehensive income and net income     0 $ 0 $ 0 0  
Accumulated other comprehensive income     $ 0   $ 0   $ 0
Executive Officer [Member]              
Significant Accounting Policies [Line Items]              
Restricted stock expense           $ 3,203,000