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Stockholders' Equity and Stock Plans - Narrative (Details) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |
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Jan. 19, 2018 $ / shares | Sep. 30, 2015 $ / shares shares | Nov. 30, 2011 investor | Dec. 31, 2017 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) shares | Jul. 23, 2017 $ / shares shares | Jul. 06, 2017 | May 16, 2017 shares | Nov. 01, 2011 $ / shares shares | May 11, 2010 shares | Jul. 01, 2007 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares withheld for tax withholding and exercise of options |  |  |  | 12,208 | 0 | 0 |  |  |  |  |  |
Value of shares withheld for tax withholding and exercise of options | $ |  |  |  | $ 801 |  |  |  |  |  |  |  |
Shares withheld for tax withholding and exercise of options, weighted average price (usd per share) | $ / shares |  |  |  | $ 65.63 |  |  |  |  |  |  |  |
Total compensation cost for share-based payment arrangements | $ |  |  |  | $ 1,300 | $ 994 | $ 636 |  |  |  |  |  |
Share-based compensation income tax benefit recognized | $ |  |  |  | 293 | 318 | 194 |  |  |  |  |  |
Unrecognized compensation expense | $ |  |  |  | $ 1,500 |  |  |  |  |  |  |  |
Period for recognizing unrecognized compensation expense |  |  |  | 2 years 1 month 6 days |  |  |  |  |  |  |  |
Excess tax benefits recorded as a reduction to income tax expense | $ |  |  |  | $ 214 |  |  |  |  |  |  |  |
Tax benefit realized from disqualifying dispositions of incentive stock options | $ |  |  |  |  | $ 70 | 49 |  |  |  |  |  |
Percentage of share ownership defining an acquiring person |  |  |  |  |  |  |  | 10.00% |  |  |  |
Preferred stock, no par value (in dollars per share) | $ / shares |  |  |  | $ 0 | $ 0 |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  | 5,000,000 | 5,000,000 |  |  |  |  |  |  |
Number of common stock shares authorized to be purchased by warrant |  | 157,711 |  |  |  |  |  |  |  | 154,242 |  |
Number of institutional investors that purchased warrant | investor |  |  | 2 |  |  |  |  |  |  |  |  |
Net issuance of shares of common stock from cashless exercise (in shares) |  | 70,591 |  |  |  |  |  |  |  |  |  |
Subsequent event |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Dividends declared per common share (usd per share) | $ / shares | $ 0.29 |  |  |  |  |  |  |  |  |  |  |
Stock options |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total grant-date fair value of option shares vested | $ |  |  |  | $ 449 | $ 282 | 202 |  |  |  |  |  |
Stock options | During 2006 through 2014 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 5 years |  |  |  |  |  |  |  |
Expiration period of grants |  |  |  | 10 years |  |  |  |  |  |  |  |
Stock options | During 2006 through 2014 | Vesting Rate, Year One |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | During 2006 through 2014 | Vesting Rate, Year Two |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | During 2006 through 2014 | Vesting Rate, Year Three |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | During 2006 through 2014 | Vesting Rate Year Four |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | During 2006 through 2014 | Vesting Rate Year Five |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | Prior to 2016 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 4 years |  |  |  |  |  |  |  |
Expiration period of grants |  |  |  | 7 years |  |  |  |  |  |  |  |
Stock options | Prior to 2016 | Immediately Upon Grant |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | Prior to 2016 | Vesting Rate, Year One |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | Prior to 2016 | Vesting Rate, Year Two |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | Prior to 2016 | Vesting Rate, Year Three |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | Prior to 2016 | Vesting Rate Year Four |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Stock options | After 2014 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 33.00% |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 3 years |  |  |  |  |  |  |  |
Expiration period of grants |  |  |  | 10 years |  |  |  |  |  |  |  |
Stock options | During 2016 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 33.00% |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 3 years |  |  |  |  |  |  |  |
Expiration period of grants |  |  |  | 10 years |  |  |  |  |  |  |  |
Restricted stock award |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total grant-date fair value of option shares vested | $ |  |  |  | $ 473 | $ 380 | $ 262 |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 5 years |  |  |  |  |  |  |  |
Expiration period of grants |  |  |  | 10 years |  |  |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 | Vesting Rate, Year One |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 | Vesting Rate, Year Two |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 | Vesting Rate, Year Three |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 | Vesting Rate Year Four |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Restricted stock award | During 2006 through 2014 | Vesting Rate Year Five |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |
Performance shares |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  | 3 years |  |  |  |  |  |  |  |
Minimum | Performance shares |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 0.00% |  |  |  |  |  |  |  |
Maximum | Performance shares |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  | 200.00% |  |  |  |  |  |  |  |
Director Stock Plan, 2010 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares approved to be issued in common stock |  |  |  |  |  |  |  |  |  |  | 150,000 |
Number of shares available for future grants under plan |  |  |  | 110,433 |  |  |  |  |  |  |  |
Employee Stock Purchase Plan, 2007 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares approved to be issued in common stock |  |  |  |  |  |  |  |  |  |  |  | 200,000
Number of shares available for future grants under plan |  |  |  | 192,453 |  |  |  |  |  |  |  |
Discount from closing market price at end of each quarter |  |  |  | 500.00% |  |  |  |  |  |  |  |
Employee Stock Purchase Plan, 2007 | Minimum |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved payroll deduction to purchase shares, percentage |  |  |  | 100.00% |  |  |  |  |  |  |  |
Employee Stock Purchase Plan, 2007 | Maximum |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved payroll deduction to purchase shares, percentage |  |  |  | 1500.00% |  |  |  |  |  |  |  |
The 2017 Equity Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of shares available for future grants under plan |  |  |  | 108,981 |  |  |  |  | 118,668 |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of warrant to purchase common stock (in shares) | $ / shares |  | $ 26.63 |  |  |  |  |  |  |  |  |  |
Common Stock | U.S. Treasury Capital Purchase Program (TCPP) |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of warrant to purchase common stock (in shares) | $ / shares |  |  |  |  |  |  |  |  |  | $ 27.23 |  |
Common Stock | Director Stock Plan, 2010 |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares awarded in period from plan |  |  |  | 2,878 | 4,607 | 5,295 |  |  |  |  |  |
Series A Junior Participating Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, no par value (in dollars per share) | $ / shares |  |  |  | $ 0 |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  | 1,000,000 |  |  |  |  |  |  |  |
Exercise price of warrant to purchase common stock (in shares) | $ / shares |  |  |  |  |  |  | $ 9,000 |  |  |  |  |
Number of shares each right entitles holder to purchase |  |  |  |  |  |  | 0.01 |  |  |  |  |

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + 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 (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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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 Discount rate from fair value on purchase date that participants pay for shares. + 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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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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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- 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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- Definition Percentage of vesting of share-based compensation awards. + 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 Period from grant date that an equity-based award expires, 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)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock. + 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) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer. + References No definition available. + Details
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