Schedule II - Valuation and Qualifying Accounts (Tables)	12 Months Ended
Dec. 31, 2018
Notes Tables
Summary of Allowance for Doubtful Accounts and Revenue Adjustments [Table Text Block]	<div style="display: inline; font-family: times new roman; font-size: 10pt"><table cellpadding="0" cellspacing="0" style="border-collapse: collapse; min-; min-width: 700px;"> <tr style="vertical-align: bottom"> <td style="white-space: nowrap; font-size: 10pt; text-align: center"> </td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2018</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2017</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2016</td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="width: 55%; font-size: 10pt; text-align: left">Balance at beginning of year</td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">652</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">567</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">499</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; text-align: left; padding-left: 10pt">Provision for bad debt</td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(50</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">116</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">126</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="font-size: 10pt; text-align: left; padding-bottom: 1pt; padding-left: 10pt">Write-offs, net of recoveries</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(38</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(31</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(58</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; text-align: left; padding-bottom: 2.25pt">Balance at end of year</td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">564</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">652</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">567</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> </tr> </table></div>

Schedule II - Valuation and Qualifying Accounts (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Allowance for Doubtful Accounts and Revenue Adjustments [Table Text Block]

<div style="display: inline; font-family: times new roman; font-size: 10pt"><table cellpadding="0" cellspacing="0" style="border-collapse: collapse; min-; min-width: 700px;"> <tr style="vertical-align: bottom"> <td style="white-space: nowrap; font-size: 10pt; text-align: center"> </td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2018</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2017</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt; text-align: center"> </td> <td colspan="3" style="white-space: nowrap; font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2016</td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="width: 55%; font-size: 10pt; text-align: left">Balance at beginning of year</td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">652</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">567</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left">$</td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">499</div></td> <td style="white-space: nowrap; width: 1%; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; text-align: left; padding-left: 10pt">Provision for bad debt</td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(50</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">116</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">126</div></td> <td style="white-space: nowrap; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="font-size: 10pt; text-align: left; padding-bottom: 1pt; padding-left: 10pt">Write-offs, net of recoveries</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(38</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(31</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">(58</div></td> <td style="white-space: nowrap; border-bottom: Black 1pt solid; font-size: 10pt; text-align: left">)</td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; text-align: left; padding-bottom: 2.25pt">Balance at end of year</td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">564</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">652</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left">$</td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">567</div></td> <td style="white-space: nowrap; border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> </tr> </table></div>