Quarterly report pursuant to Section 13 or 15(d)

Equity Incentive Plan (Details)

v3.8.0.1
Equity Incentive Plan (Details) - Second Restated 2009 Equity Incentive Plan [Member] - $ / shares
 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted common shares granted during period under equity incentive plan (in shares) 671,845 1,009,630
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) $ 17.60 $ 15.11
Award vesting period of restricted common shares granted during period under equity incentive plan 3 years  
Director [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted common shares granted during period under equity incentive plan (in shares) 34,559 40,869
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) $ 19.82 $ 16.86
Key Employees [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted common shares granted during period under equity incentive plan (in shares) 637,286 968,761
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) $ 17.48 $ 15.04
Common stock share price (in usd per share) $ 20.16