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Employee Plans - Summary of Information Regarding the Common Shares Issued Under the ESPP (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Employee Service Share Based Compensation Aggregate Disclosures [Abstract] |  |  |
Shares issued | 68,286 | 63,909 | 68,462
Issuance price ranges, Minimum | $ 52.79 | $ 51.85 | $ 63.70
Issuance price ranges, Maximum | $ 58.06 | $ 63.37 | $ 65.90
Issuance proceeds | $ 3,744 | $ 3,686 | $ 4,404

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- Definition Represents the maximum price that employees purchase common stock for under the employee purchase plan during the year. + References No definition available. + Details
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- Definition Represents the minimum price that employees purchase common stock for under the employee purchase plan during the year. + References No definition available. + Details
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- References No definition available. + Details
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- Definition Amount of cash inflow from issuance of shares under share-based compensation arrangement, excluding stock option exercises. + 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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- Definition Number of share instruments newly issued under a share-based compensation 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 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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Period Type: | duration