Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

v3.10.0.1
Shareholders' Equity (Details)
$ / shares in Units, shares in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
$ / shares
shares
Sep. 30, 2018
USD ($)
$ / shares
shares
Sep. 30, 2017
USD ($)
May 04, 2018
USD ($)
agreements
Class of Stock [Line Items]        
Number of separate equity distribution agreements | agreements       8
Proceeds from issuance of common shares   $ 35,472,000 $ 113,225,000  
Shares issued under dividend reinvestment program (in shares) | shares 18      
Shares issued under dividend reinvestment program, weighted share price per share | $ / shares $ 30.68 $ 29.29    
Value of shares issued under dividend reinvestment program $ 600,000 $ 1,811,000    
Common Stock [Member]        
Class of Stock [Line Items]        
Capital shares reserved for future issuances       $ 250,000,000.0
Common shares issued | shares 1,200 1,165    
Shares issued, average price per share | $ / shares $ 31.18 $ 31.18    
Shares issued under dividend reinvestment program (in shares) | shares   74    
Value of shares issued under dividend reinvestment program   $ 1,000    
Additional Paid-in Capital [Member]        
Class of Stock [Line Items]        
Proceeds from issuance of common shares $ 35,500,000 35,500,000    
Value of shares issued under dividend reinvestment program   $ 1,810,000