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Stock Incentive Plans - Performance Stock Units (Details) - Performance Stock Units - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Number of Units      
Number of shares, Beginning Balance (in shares) 785,797 686,684 676,359
Number of shares, Granted (in shares) 293,111 266,009 310,398
Number of shares, Additional units from dividends 35,197 33,478 38,324
Number of shares, Vested (in shares) (218,514) (200,374) (242,096)
Number of shares, Forfeited (in shares) (113,668)   (96,301)
Number of shares, Ending Balance (in shares) 781,923 785,797 686,684
Weighted- Average Grant Date Fair Value      
Weighted-average grant date fair value, Beginning balance (in dollars per share) $ 10.42 $ 10.65 $ 11.41
Weighted-average grant date fair value, Granted (in dollars per share) 9.82 11.04 8.54
Weighted-average grant date fair value, Additional shares from dividends (in dollars per share) 11.24 11.17 9.37
Weighted-average grant date fair value, Vested (in dollars per share) 11.98 12.15 9.85
Weighted-average grant date fair value, Forfeited (in dollars per share) 9.86   10.74
Weighted-average grant date fair value, Ending balance (in dollars per share) $ 11.19 $ 10.42 $ 10.65
Stock of common stock earned for the PSUs vested in 2016 (as a percent) 51.75%   89.50%
Percentage of total stockholder return for payout of shares (as a percent) 30.00% 30.00%  
Share based payment, vesting period (years) 3 years 3 years