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Description of Business and Summary of Significant Accounting Policies (Employee Savings Plans) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items] |  |  |
401(k) plan employer matching contribution | $ 7.1 | $ 6.8 | $ 6.8
401(k) plan matching contribution graded vesting period | 3 years |  |
Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member] |  |  |
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items] |  |  |
Matching contributions to employee participants | $ 0.7 | 0.7 | $ 0.6
Deferred compensation arrangement with individual matching contribution annual vesting years two and three | 33.00% |  |
Deferred compensation arrangement with individual matching contribution annual vesting portion, year one | 33.00% |  |
Employer contributions vesting periods (in years) | 3 years |  |
Balances due to participants | $ 78.1 | $ 68.2 |

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- Definition Portion of employer's matching contributions to a deferred compensation plan that is vested and credited to participants on the first business day of the subsequent calendar year. + References No definition available. + Details
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- Definition Portion of employer's matching contributions to a deferred compensation plan that is vested and credited to participants on the second and third anniversaries of the first business day of the subsequent calendar year after the date of the contribution. + References No definition available. + Details
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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. + Details
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- Definition Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, 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 710 -SubTopic 10 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date. + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Details
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