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Stockholders' Equity (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 20, 2018 | Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Class of Stock [Line Items] |  |  |  |
Cash dividends to common stockholders |  | $ 2,015,000 | $ 1,655,000 | $ 6,896,000
Cash dividends per common share (usd per share) |  | $ 0.29 | $ 0.27 |
Shares withheld for tax withholding and exercise of options |  | 19,606 | 4,715 |
Amount of shares withheld for tax withholding and exercise of options |  | $ 1,400,000 | $ 324,000 |
Shares withheld for tax withholding and exercise of options, weighted average price (usd per share) |  | $ 70.36 | $ 68.80 |
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% |  |
Subsequent event |  |  |  |
Class of Stock [Line Items] |  |  |  |
Dividends declared per common share (usd per share) | $ 0.31 |  |  |
Share Repurchase Program, amount approved to repurchase | $ 25,000,000.0 |  |  |
Retained Earnings |  |  |  |
Class of Stock [Line Items] |  |  |  |
Cash dividends to common stockholders |  | $ 2,015,000 |  | $ 6,896,000
Reclassification from AOCI to retained earnings for stranded income tax effects |  | $ 638,000 |  |

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