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Stock-based Payment Arrangements (Tables) | 12 Months Ended
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Dec. 31, 2019
Share-based Payment Arrangement [Abstract] |
Assumptions Used in Computing Fair Value of All Options Granted | The fair value of each option granted is estimated on the grant date using the Black-Scholes option pricing model. This model requires management to make certain assumptions, including the expected life of the option, the risk-free rate of interest, the expected volatility and the expected dividend yield. The following assumptions were made in estimating 2019 fair values:
Expected dividends | 2.34 | %
Expected volatility | 21.44 | %
Risk-free interest rate | 2.2 | %
Expected term (in years) | 6.5
Summary of Stock Option Activity | The following table represents stock option activity for the years indicated.
Options |  | Number of Options |  | Weighted- Average Exercise Price |  | Weighted- Average Grant Date Fair Value |  | Weighted- Average Remaining Contractual Term (Years)
Outstanding as of December 31, 2016 |  | 484,688 |  |  | $ | 14.55 |  |  | $ | 4.17 |  |  |
Granted |  | 28,290 |  |  | 35.25 |  |  | 7.14 |  |  |
Exercised |  | (103,240) |  |  | 11.73 |  |  | 3.81 |  |  |
Forfeited |  | (1,260) |  |  | 30.56 |  |  | 5.95 |  |  |
Outstanding as of December 31, 2017 |  | 408,478 |  |  | $ | 16.64 |  |  | $ | 4.46 |  |  | 3.7
Granted |  | 28,790 |  |  | 44.88 |  |  | 10.35 |  |  |
Exercised |  | (83,348) |  |  | 12.90 |  |  | 3.99 |  |  |
Forfeited |  | (1,550) |  |  | 28.34 |  |  | 5.59 |  |  |
Outstanding as of December 31, 2018 |  | 352,370 |  |  | $ | 19.78 |  |  | $ | 5.05 |  |  | 3.6
Granted |  | 37,780 |  |  | 35.78 |  |  | 6.52 |  |  |
Exercised |  | (198,786) |  |  | 12.52 |  |  | 3.85 |  |  |
Forfeited |  | (10,834) |  |  | 33.13 |  |  | 6.79 |  |  |
Outstanding as of December 31, 2019 |  | 180,530 |  |  | $ | 30.32 |  |  | $ | 6.57 |  |  | 6.6
Exercisable as of December 31, 2017 |  | 315,912 |  |  | $ | 13.23 |  |  | $ | 4.09 |  |  | 2.3
Exercisable as of December 31, 2018 |  | 258,319 |  |  | 14.65 |  |  | 4.27 |  |  | 2.0
Exercisable as of December 31, 2019 |  | 86,401 |  |  | 24.73 |  |  | 5.94 |  |  | 5.1
Unvested Restricted Stock Activity | The following table represents unvested restricted stock activity for the years indicated.
Restricted Stock |  | Number of Shares |  | Weighted-Average Grant Date Fair Value
Balance, December 31, 2016 |  | 48,557 |  |  | $ | 24.89 |
Granted |  | 18,660 |  |  | 37.02 |
Forfeited |  | (400) |  |  | 28.84 |
Released |  | (12,182) |  |  | 23.76 |
Balance, December 31, 2017 |  | 54,635 |  |  | $ | 29.26 |
Granted |  | 16,345 |  |  | 44.88 |
Forfeited |  | (195) |  |  | 30.79 |
Released |  | (15,405) |  |  | 27.46 |
Balance, December 31, 2018 |  | 55,380 |  |  | $ | 34.36 |
Granted |  | 18,745 |  |  | 35.84 |
Forfeited |  | (4,251) |  |  | 36.01 |
Released |  | (18,711) |  |  | 31.79 |
Balance, December 31, 2019 |  | 51,163 |  |  | $ | 35.71 |

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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=116856206&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=116856206&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=116856206&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=116856206&loc=d3e5070-113901 + Details
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