Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

v3.8.0.1
Shareholders' Equity (Details)
3 Months Ended
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2017
USD ($)
Jun. 23, 2015
USD ($)
agreements
Class of Stock [Line Items]      
Number of separate equity distribution agreements | agreements     4
Net proceeds from equity issuances $ 0 $ 29,959,000  
Shares issued under dividend reinvestment program $ 717,000    
Common Stock [Member]      
Class of Stock [Line Items]      
Capital shares reserved for future issuances     $ 200,000,000.0
Shares issued under dividend reinvestment program (in shares) | shares 37,079    
Stock issued during period, weighted share price, Dividend Reinstated Plan | $ / shares $ 28.16    
Shares issued under dividend reinvestment program $ 0    
Additional Paid-in Capital [Member]      
Class of Stock [Line Items]      
Shares issued under dividend reinvestment program $ 717,000