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Stock Based Compensation (Details) - Employee Stock Option [Member] - $ / shares | 3 Months Ended | 12 Months Ended
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Mar. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Shares - Nonvested, Beginning Balance (in shares) | 27,423 | 30,690
Shares - Granted (in shares) | 7,407 | 4,433
Shares - Vested (in shares) | (3,302) | (7,700)
Shares - Forfeited (in shares) | 0 | 0
Shares - Nonvested, Ending Balance (in shares) | 31,528 | 27,423
Weighted-Average Grant Date Fair Value - Nonvested, Beginning Balance (in dollars per share) | $ 32.58 | $ 28.51
Weighted-Average Grant Date Fair Value - Granted (in dollars per share) | 43.00 | 43.50
Weighted-Average Grant Date Fair Value - Vested (in dollars per share) | 27.26 | 22.64
Weighted-Average Grant Date Fair Value - Forfeited (in dollars per share) | 0 | 0
Weighted-Average Grant Date Fair Value - Nonvested, Ending Balance (in dollars per share) | $ 35.58 | $ 32.58

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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 Gross number of share options (or share units) granted during the period. + References No definition available. + 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average grant-date fair value of non-vested options forfeited. + References No definition available. + Details
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- Definition Weighted average grant-date fair value of options vested. + References No definition available. + Details
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