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Stock Award Plans, All Plans Options and Restricted Stock Award Activity (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Intrinsic value of stock options exercised | $ 745,000 | $ 1,655,000 | $ 6,709,000
Tax benefit from stock options exercised | 210,000 | 410,000 | 2,073,000
Intrinsic value of restricted stock vesting | 5,649,000 | 5,917,000 | 12,936,000
Tax benefit from restricted stock vesting | $ 1,590,000 | $ 1,464,000 | $ 3,997,000
Fair value of stock options granted (in dollars per share) | $ 20.19 | $ 22.77 | $ 23.53
Fair value of stock options granted | $ 2,314,000 | $ 2,666,000 | $ 2,787,000
Employee Stock Award Plan [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Intrinsic value of restricted stock vesting | 5,172,000 | 1,727,000 |
Tax benefit from restricted stock vesting | 1,455,000 | $ 427,000 |
Stock Options [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Unrecognized compensation cost related to unvested awards | $ 2,136,000 |  |
Weighted average period of recognition in years | 1 year 8 months 12 days |  |
Fair Value Assumptions [Abstract] |  |  |
Dividend yield | 0.00% | 0.00% | 0.00%
Average risk-free interest rate | 1.30% | 2.50% | 2.70%
Stock price volatility | 28.00% | 28.00% | 27.00%
Estimated option term | 5 years 3 months 18 days | 5 years 3 months 18 days | 5 years 6 months
Restricted Stock [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Unrecognized compensation cost related to unvested awards | $ 1,468,000 |  |
Weighted average period of recognition in years | 7 months 6 days |  |
Restricted Stock [Member] | Employee Stock Award Plan [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Vesting (in shares) | 48,450 |  |
RSUs [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Vesting (in shares) |  |  | 0
Unrecognized compensation cost related to unvested awards | $ 13,298,000 |  |
Weighted average period of recognition in years | 3 years 3 months 18 days |  |
RSUs [Member] | Employee Stock Award Plan [Member] |  |  |
Share-based Compensation Plans Combined Disclosure [Abstract] |  |  |
Vesting (in shares) | 64,039 |  |

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- Definition Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise. + References No definition available. + Details
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- Definition Amount of cost not yet recognized for nonvested award under share-based payment arrangement. + 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 (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + 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)(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + 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)(iv) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + 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)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Intrinsic value of vested award under share-based payment arrangement. Excludes share and unit options. + References No definition available. + Details
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- Definition Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + 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)(i) -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 S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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