Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plan Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity (Details)

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Equity Incentive Plan Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Number of nonvested restricted common shares outstanding at beginning of period (in shares) 1,593,701 1,284,010  
Weighted average grant date fair value of nonvested restricted common shares outstanding at beginning of period (in usd per share) $ 15.81 $ 17.15  
Number of restricted common shares granted during period under equity incentive plan (in shares) 515,282 996,924  
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) $ 14.28 $ 14.96  
Number of restricted common shares vested during period (in shares) (942,874) (673,118)  
Weighted average grant date fair value of restricted common shares vested during period (in usd per share) $ (14.63) $ (17.12)  
Number of restricted common shares forfeited during period (in shares) (103,208) (14,115)  
Weighted average grant date fair value of restricted common shares forfeited during period (in usd per share) $ (15.52) $ (15.59)  
Number of nonvested restricted common shares outstanding at end of period (in shares) 1,062,901 1,593,701 1,284,010
Weighted average grant date fair value of nonvested restricted common shares outstanding at end of period (in usd per share) $ 16.14 $ 15.81 $ 17.15
Compensation costs related to restricted common stock $ 9.2 $ 13.0 $ 11.3