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Stock-Based Compensation (Nonvested Performance-based Award Activity) (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Incentive Stock Awards [Member] |  |  |
Non-vested PVS Awards [Roll Forward] |  |  |
Granted at target level | 1,800 | 2,400 | 1,500
Forfeited | (800) | (800) | (200)
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Granted at target level | $ 86.93 | $ 59.64 | $ 51.53
Performance-Vesting Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Number of shares to be issued upon conversion | 166,439 |  |
Average remaining term of shares issued at conversion | 1 year |  |
Non-vested PVS Awards [Roll Forward] |  |  |
Outstanding, Beginning | 378,062 | 422,726 | 470,719
Granted at target level | 92,045 | 115,035 | 147,908
Adjustments above/(below) target | 11,369 | (19,339) | (132,444)
Vested and converted | (116,684) | (173,364) | (318,337)
Forfeited | (110) | (5,674) | (10,008)
Outstanding, Ending | 341,944 | 378,062 | 422,726
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Outstanding, Beginning (in usd per share) | $ 54.47 | $ 45.60 | $ 30.93
Granted at target level | 84.01 | 60.47 | 55.49
Adjustments above/(below) target | 42.85 | 38.71 | 22.97
Vested and converted | 50.06 | 59.64 | 51.53
Forfeited | 73.64 | 49.86 | 41.84
Outstanding, Ending (in usd per share) | $ 64.38 | $ 54.47 | $ 45.60
Performance-Vesting Units [Member] |  |  |
Non-vested PVS Awards [Roll Forward] |  |  |
Outstanding, Beginning | 2,451 | 29,196 | 55,509
Granted at target level | 598 | 419 | 1,386
Adjustments above/(below) target | 107 | (2,858) | (19,315)
Vested and converted | (970) | (29,032) | (47,014)
Forfeited | 0 | (990) | 0
Outstanding, Ending | 1,972 | 2,451 | 29,196
Non-vested PVS Awards, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Outstanding, Beginning (in usd per share) | $ 25.28 | $ 32.07 | $ 26.15
Granted at target level | 83.47 | 59.64 | 54.14
Adjustments above/(below) target | 66.61 | 30.80 | 22.07
Vested and converted | 86.93 | 59.64 | 51.53
Forfeited | 0.00 | 50.55 | 0.00
Outstanding, Ending (in usd per share) | $ 92.25 | $ 25.28 | $ 32.07
Minimum [Member] | Performance-Vesting Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Actual payout range | 0.00% |  |
Minimum [Member] | Performance-Vesting Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Actual payout range | 0.00% |  |
Maximum [Member] | Performance-Vesting Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Actual payout range | 200.00% |  |
Maximum [Member] | Performance-Vesting Units [Member] |  |  |
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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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