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Stock-Based Compensation Status of Nonvested Restricted Shares (Details) - Restricted Stock [Member]
12 Months Ended
Dec. 31, 2019
$ / shares
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Nonvested as of January 1, 2019 | shares 187,777
Issued | shares 173,174
Vested | shares (125,381)
Forfeited | shares (1,692)
Nonvested as of December 31, 2019 | shares 233,878
Nonvested as of January 1, 2019 | $ / shares $ 88.79
Issued | $ / shares 88.59
Vested | $ / shares 74.35
Forfeited | $ / shares 95.44
Nonvested as of December 31, 2019 | $ / shares $ 96.33