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Equity Incentive Plan - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Feb. 28, 2019
Feb. 28, 2018
May 31, 2016
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized (in shares)       7,500,000      
Common shares available for future grant (in shares)       762,744      
Restricted share awards              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Unvested restricted shares       1,252,228 940,202 740,792 700,325
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value       $ 15.17 $ 20.21 $ 21.89 $ 22.88
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period       801,463 530,436 592,673  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value       $ 11.95 $ 18.69 $ 21.42  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period       (480,444) (312,131) (438,881)  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value       $ 19.59 $ 21.63 $ 22.92  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period       (8,993) (18,895) (113,325)  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value       $ 18.80 $ 20.03 $ 21.58  
Share-based compensation expense       $ 8.7 $ 8.6 $ 10.2  
Total unrecognized compensation costs       $ 13.7      
Weighted-average period of recognition of unrecognized share-based compensation expense       2 years 4 months 24 days      
Total fair value of shares vested       $ 5.2 $ 5.5 $ 9.5  
2017 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period           264,000  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value           $ 13.99  
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate           2.42%  
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate           27.44%  
2018 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period         260,000    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value         $ 19.16    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate         2.52%    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate         27.19%    
Performance units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense       3.5 $ 2.9 $ 2.1  
Total unrecognized compensation costs       $ 7.1      
Weighted-average period of recognition of unrecognized share-based compensation expense       2 years 3 months 18 days      
2019 Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period       489,000      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value       $ 12.06      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period   4 years          
Share Based Compensation Arrangement by Share Based Payment Award, Performance Based Vesting Period 3 years            
Share Based Compensation Arrangement by Share Based Payment Award, Time Based Vesting Period 1 year   1 year        
Share-based compensation arrangement, by share based payment award, vesting rights percentage immediately 50.00%            
Share-based compensation arrangement, by share-based payment award vesting rights, percentage after one year 50.00%            
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate       1.08%      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate       23.46%      
Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Share Based Awards Other Than Options Percentage Of Grant Date Fair Value Recognized Over Three Years 50.00%            
Employee Service Share Based Compensation Nonvested Awards For First Fifty Percent Compensation Cost Not Yet Recognized Period For Recognition 3 years            
Employee Service Share Based Compensation Nonvested Awards For Remaining Fifty Percent Compensation Cost Not Yet Recognized Period For Recognition 50.00%            
Employee Service Share Based Compensation Nonvested Awards For Remaining Fifty Percent Cost Not Yet Recognized, Period For Recognition 4 years            
Minimum | 2016 Performance Units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period     25        
Minimum | 2017 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period           25  
Minimum | 2018 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period         25    
Minimum | 2019 Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period 0.00%            
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period       25      
Maximum | 2016 Performance Units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period     150        
Maximum | 2017 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period           150  
Maximum | 2018 Performance Shares              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period         150    
Maximum | 2019 Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period 200.00%            
Shared-based compensation arrangement by share based payment award, conversion percentage of units granted in period       200