Basis of Presentation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Weighted average basic shares outstanding (shares)	6,123	6,083	6,109	6,070
Potentially dilutive common shares related to:
Stock options (shares)	53	27	55	30
Unvested restricted stock awards (shares)	15	7	15	6
Weighted average diluted shares outstanding (shares)	6,191	6,117	6,179	6,106
Net income	$ 5,132	$ 6,964	$ 14,866	$ 17,447	$ 23,134
Basic EPS (usd per share)	$ 0.84	$ 1.14	$ 2.43	$ 2.87
Diluted EPS (usd per share)	$ 0.83	$ 1.14	$ 2.41	$ 2.86
Weighted average anti-dilutive shares not included in the calculation of diluted EPS (shares)	23	71	19	65

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Number of additional shares included in diluted EPS for potentially dilutive effect of nonvested equity-based payment award containing forfeitable rights to dividends or dividend equivalents, whether paid or unpaid.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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