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Stock-Based Compensation - Nonvested Performance-based Award Activity (Details) - $ / shares | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Non-Employee Directors | Deferred Compensation, Share-based Payments |  |  |
Non-vested PSU Awards [Roll Forward] |  |  |
Granted at target level (in shares) | 10,302 |  |
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Granted at target level (in dollars per share) | $ 194.29 |  |
Incentive Stock Awards |  |  |
Non-vested PSU Awards [Roll Forward] |  |  |
Granted at target level (in shares) | 350 | 1,300 | 1,500
Forfeited (in shares) | 0 | 0 | (200)
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Granted at target level (in dollars per share) | $ 156.49 | $ 106.14 | $ 93.00
Stock-settled PSU awards |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Number of shares to be issued upon conversion (in shares) | 92,792 |  |
Average remaining term of shares issued at conversion | 1 year |  |
Non-vested PSU Awards [Roll Forward] |  |  |
Outstanding, beginning (in shares) | 264,622 | 296,037 | 341,944
Granted at target level (in shares) | 53,659 | 84,309 | 102,307
Adjustments above/(below) target (in shares) | (14,004) | (50,556) | (2,284)
Vested and converted (in shares) | (70,074) | (48,964) | (121,984)
Forfeited (in shares) | (11,404) | (16,204) | (23,946)
Outstanding, ending (in shares) | 222,799 | 264,622 | 296,037
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Outstanding, beginning (in dollars per share) | $ 92.80 | $ 76.84 | $ 64.38
Granted at target level (in dollars per share) | 177.31 | 103.40 | 90.45
Adjustments above/(below) target (in dollars per share) | 77.02 | 83.89 | 33.86
Vested and converted (in dollars per share) | 173.22 | 102.51 | 93.00
Forfeited (in dollars per share) | 104.43 | 69.09 | 68.65
Outstanding, ending (in dollars per share) | $ 116.37 | $ 92.80 | $ 76.84
Cash-Settled PSU Awards |  |  |
Non-vested PSU Awards [Roll Forward] |  |  |
Outstanding, beginning (in shares) | 1,981 | 1,592 | 1,972
Granted at target level (in shares) | 732 | 806 | 560
Adjustments above/(below) target (in shares) | (99) | (206) | (30)
Vested and converted (in shares) | (502) | (211) | (910)
Forfeited (in shares) | 0 | 0 | 0
Outstanding, ending (in shares) | 2,112 | 1,981 | 1,592
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Outstanding, beginning (in dollars per share) | $ 93.28 | $ 79.48 | $ 92.25
Granted at target level (in dollars per share) | 190.71 | 102.51 | 89.64
Adjustments above/(below) target (in dollars per share) | 74.43 | 56.95 | 41.53
Vested and converted (in dollars per share) | 173.22 | 102.51 | 93.00
Forfeited (in dollars per share) | 0 | 0 | 0
Outstanding, ending (in dollars per share) | $ 130.13 | $ 93.28 | $ 79.48
Restricted Stock |  |  |
Non-vested PSU Awards [Roll Forward] |  |  |
Granted at target level (in shares) | 8,721 | 13,308 | 15,942
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Granted at target level (in dollars per share) | $ 200.35 | $ 116.39 | $ 96.77
Minimum | Stock-settled PSU awards |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Actual payout range | 0.00% |  |
Maximum | Stock-settled PSU awards |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Actual payout range | 200.00% |  |

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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting 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 (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event. + 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)(iii)(3) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options. + 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)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting 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 (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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