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Equity - Share-Based Compensation Narrative (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares
Class of Stock [Line Items] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number | shares | 163,272 |  |
Proceeds from Stock Options Exercised | $ 200,000 | $ 500,000 | $ 1,700,000
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options | 2,600,000 | 3,600,000 | 800,000
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options | $ (2,600,000) | $ (3,100,000) | $ (600,000)
Stock Issued During Period, Shares, Other | shares | 698 | 1,130 | 491
Stock Issued During Period, Value, Other | $ 41,000 | $ 41,000 | $ 14,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price | $ / shares | $ 32.95 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $ 14,800,000 | 17,400,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | 3,800,000 | $ 7,600,000 | $ 900,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $ 2,300,000 |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | 1 year 8 months 5 days |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares | $ 44.93 | $ 25.11 | $ 17.97
Allocated Share-based Compensation Expense | $ 2,700,000 | $ 3,300,000 | $ 3,300,000
Common Class C, Non-Voting [Member] |  |  |
Class of Stock [Line Items] |  |  |
Number of Board of Directors | 4 | 4 | 4

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- Definition Changes in additional paid in capital related to exercise of share-based payments awards (such as stock options) and the amount of recognized equity-based compensation during the period (such as nonvested shares). + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + 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 (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=96867065&loc=SL79508275-113901 + 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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