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Stock Option Plans - Narrative (Details) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2018 compensation_plan shares | Mar. 29, 2018 $ / shares | Dec. 31, 2017 shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |  |  |
Number of stock option plans | compensation_plan | 2 |  |
Option expiration period | 10 years |  |
Option vesting period | 4 years |  |
Closing share price (in usd per share) | $ / shares |  | $ 50.97 |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted (in shares) | 905,670 |  | 913,320
Weighted average remaining contractual life of the Company's outstanding options | 7 years 3 months 9 days |  |
Weighted average remaining contractual life of the Company's exercisable options | 6 years 3 months 4 days |  |
2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted (in shares) | 189,375 |  |
2016 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted (in shares) | 213,375 |  |
2017 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted (in shares) | 232,500 |  |

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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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