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Share-based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Share-based Compensation [Abstract] |
Schedule of Assumptions Used |
​ | ​
​ | 2018
​ | ​
Expected term (in years) | 6.4
Risk-free interest rate | 2.64%
Expected volatility | 33.30%
Dividend yield | 2.87%
Stock Option Activity | The number of stock options and weighted-average exercise prices as of December 31, 2020 and 2019 are as follows:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | 2020 | ​ | 2019
​ | Awards | ​ | Weighted-Average Exercise Price | ​ | Awards | ​ | Weighted-Average Exercise Price
(awards in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Outstanding at beginning of period | 97 | ​ | $ | 52.53 | ​ | 107 | ​ | $ | 49.26
Exercised | (28) | ​ | ​ | 57.79 | ​ | (10) | ​ | ​ | 28.21
Forfeited | (8) | ​ | ​ | 68.45 | ​ | - | ​ | ​ | -
Outstanding at end of the period | 61 | ​ | $ | 48.19 | ​ | 97 | ​ | $ | 52.53
Exercisable at end of the period | 44 | ​ | $ | 39.98 | ​ | 52 | ​ | $ | 40.96
Restricted Stock Activity |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | 2020 | ​ | 2019
​ | Shares | ​ | Weighted-Average Grant Date Fair Value | ​ | Shares | ​ | Weighted-Average Grant Date Fair Value
(shares in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Outstanding at beginning of period | 46 | ​ | $ | 98.28 | ​ | 57 | ​ | $ | 50.55
Granted | 43 | ​ | ​ | 113.87 | ​ | 29 | ​ | ​ | 130.89
Vested | (32) | ​ | ​ | 88.71 | ​ | (37) | ​ | ​ | 45.83
Forfeited | (7) | ​ | ​ | 108.86 | ​ | (3) | ​ | ​ | 167.48
Outstanding at end of the period | 50 | ​ | $ | 116.06 | ​ | 46 | ​ | $ | 98.28

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- Definition Tabular disclosure of the changes in outstanding nonvested restricted stock units. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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