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Stock-based Compensation and Other Employee Benefit Plans Stock-based Compensation: Incentive Award Plan and Employee Stock Purchase Plan (Range of Prices) (Details) - $ / shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | $ 4.44 |
Exercise price, high end of the range (in dollars per share) | $ 16.51 |
Options outstanding (in shares) | 132,670 |
Options outstanding - weighted average remaining contractual life (years) | 3 years 9 months 18 days | 4 years 3 months 18 days
Options outstanding - weighted average exercise price (in dollars per share) | $ 12.79 | $ 12.10
Options exercisable - at the end of period (in shares) | 132,670 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 12.79 |
$4.44 - 7.31 |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | 4.44 |
Exercise price, high end of the range (in dollars per share) | $ 7.31 |
Options outstanding (in shares) | 25,653 |
Options outstanding - weighted average remaining contractual life (years) | 1 year 7 months 6 days |
Options outstanding - weighted average exercise price (in dollars per share) | $ 6.25 |
Options exercisable - at the end of period (in shares) | 25,653 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 6.25 |
$7.39 - 7.39 |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | 7.39 |
Exercise price, high end of the range (in dollars per share) | $ 7.39 |
Options outstanding (in shares) | 3,500 |
Options outstanding - weighted average remaining contractual life (years) | 2 years 3 months 18 days |
Options outstanding - weighted average exercise price (in dollars per share) | $ 7.39 |
Options exercisable - at the end of period (in shares) | 3,500 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 7.39 |
$8.26 - 8.26 |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | 8.26 |
Exercise price, high end of the range (in dollars per share) | $ 8.26 |
Options outstanding (in shares) | 12,023 |
Options outstanding - weighted average remaining contractual life (years) | 3 years |
Options outstanding - weighted average exercise price (in dollars per share) | $ 8.26 |
Options exercisable - at the end of period (in shares) | 12,023 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 8.26 |
$10.46 - 10.46 |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | 10.46 |
Exercise price, high end of the range (in dollars per share) | $ 10.46 |
Options outstanding (in shares) | 16,494 |
Options outstanding - weighted average remaining contractual life (years) | 3 years 10 months 24 days |
Options outstanding - weighted average exercise price (in dollars per share) | $ 10.46 |
Options exercisable - at the end of period (in shares) | 16,494 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 10.46 |
$16.51 - 16.51 |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercise price, low end of the range (in dollars per share) | 16.51 |
Exercise price, high end of the range (in dollars per share) | $ 16.51 |
Options outstanding (in shares) | 75,000 |
Options outstanding - weighted average remaining contractual life (years) | 4 years 8 months 12 days |
Options outstanding - weighted average exercise price (in dollars per share) | $ 16.51 |
Options exercisable - at the end of period (in shares) | 75,000 |
Options exercisable - weighted average exercise price (in dollars per share) | $ 16.51 |

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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 The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option 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 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option 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 -Subparagraph (c)(1)(iii) -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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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option 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 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + 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 (g) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for option awards outstanding, 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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