Share-based Payments Share-based Payments (Details Textual)	3 Months Ended
Mar. 31, 2018 $ / shares shares
Performance stock units settled in stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)	0.00%
Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)	200.00%
Number of shares granted	66,000
Weighted average grant date fair value \| $ / shares	$ 317.58
Performance stock units settled in cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)	0.00%
Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)	200.00%
Number of shares granted	44,000
Number of days for calculation of average closing stock price	30 days

Maximum target number of market stock units granted based on stock performance in percent.

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- Definition

Minimum target number of market stock units granted based on stock performance in percent.

+ References

No definition available.

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- Definition

Number of days for calculation of average closing stock price.

+ References

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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

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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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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