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Basis of Presentation and Significant Accounting Policies - Fair Value Assumptions for Stock Option Pricing (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]      
Number of stock options granted (in shares) 234,248 282,040 223,208
Weighted average grant date fair value of stock options granted (in usd per share) $ 6.02 $ 6.26 $ 7.16
Weighted average assumptions:      
Risk-free interest rate 0.80% 2.50% 2.60%
Expected dividend yield 2.70% 2.90% 2.60%
Expected life, in years 5 years 1 month 6 days 5 years 4 years 9 months 18 days
Expected volatility (based on historical volatility) 22.80% 21.90% 21.50%