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Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Shares      
Outstanding at beginning of period (in shares) 574,219 490,415 407,563
Granted and fully vested (in shares) 130,065 83,804 82,852
Issued (in shares) 0 0 0
Forfeited (in shares) 0 0 0
Outstanding at end of period (in shares) 704,284 574,219 490,415
Weighted- Average Grant Date Fair Value per Share      
Outstanding at beginning of period (in dollars per share) $ 18.47 $ 17.41 $ 16.17
Granted and fully vested (in dollars per share) 15.88 24.70 23.47
Issued (in dollars per share) 0 0 0
Forfeited (in dollars per share) 0 0 0
Outstanding at end of period (in dollars per share) $ 17.99 $ 18.47 $ 17.41
Additional disclosures      
Aggregate intrinsic value $ 11.5