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Incentive Plan - Summary of Fair Value of Stock Options Granted (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Payment Arrangement [Abstract]      
Risk-free interest rate 1.03% 2.63% 2.65%
Expected option life 7 years 7 years 7 years
Expected volatility 23.00% 21.00% 21.00%
Expected dividend yield 3.33% 2.70% 2.19%
Weighted average fair value of an option share granted during the year (in dollars per share) $ 2.93 $ 4.47 $ 5.44
Intrinsic value of options exercised during the year (in shares) $ 2,499 $ 2,994 $ 8,513