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Share-Based Payments (Weighted-Average Fair Value of Options and Stock Per Share) (Details) - $ / shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Restricted Stock Units (RSUs) [Member] |  |  |
Stock, weighted average grant date fair value | $ 42.66 | $ 32.53 | $ 25.22
Employee Stock Purchase Plan [Member] |  |  |
Options, weighted average grant date fair value | 2.73 | 2.63 | 1.26
15% of grant date market value | 7.06 | 5.23 | 4.16
Total ESPP | 9.79 | 7.86 | 5.42
Agent Stock Purchase Plan [Member] |  |  |
Stock, weighted average grant date fair value | $ 5.04 | $ 3.79 | $ 2.94

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- Definition The weighted average fair value discount at grant date, for employee stock purchase plan shares issued during the period. + References No definition available. + Details
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- Definition The total weighted average fair value at grant date for employee stock purchase plan shares issued during the period. + References No definition available. + 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 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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