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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Oct. 20, 2017 | Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016 | Jul. 23, 2017 | May 16, 2017
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Cash dividends to common stockholders |  | $ 1,788 | $ 1,528 | $ 5,103 | $ 4,573 | $ 6,223 |  |
Cash dividends per common share (usd per share) |  | $ 0.29 | $ 0.25 | $ 0.83 | $ 0.75 |  |  |
Number of shares available for grant |  |  |  |  |  |  |  | 118,668
Shares withheld for tax withholding and exercise of options |  |  |  | 11,938 |  |  |  |
Amount of shares withheld for tax withholding and exercise of options |  |  |  | $ 782 |  |  |  |
Shares withheld for tax withholding and exercise of options, weighted average price (usd per share) |  |  |  | $ 65.50 |  |  |  |
Performance-based stock awards |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Vesting period of performance-based stock awards |  |  |  | 3 years |  |  |  |
Performance-based stock awards | Minimum |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Vesting percentage of performance-based awards |  |  |  | 0.00% |  |  |  |
Performance-based stock awards | Maximum |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Vesting percentage of performance-based awards |  |  |  | 200.00% |  |  |  |
Series A Junior Participating Preferred Stock |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Number of shares each right entitles holder to purchase |  |  |  |  |  |  | 0.01 |
Exercise price of right (usd per share) |  |  |  |  |  |  | $ 9,000 |
Subsequent event |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Dividends declared per common share (usd per share) | $ 0.29 |  |  |  |  |  |  |

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