Net Income (Loss) Per Share - Computation Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Income (Loss) Per Share
Net (loss) income	$ (8,965)	$ 24,467	$ (18,983)	$ 12,558
Weighted average common shares outstanding - basic	20,392	20,389	20,169	20,301
Dilutive effect of common stock equivalents		290		217
Weighted average common shares outstanding - diluted	20,392	20,679	20,169	20,518
Net (loss) income per share
Basic (in dollars per share)	$ (0.44)	$ 1.20	$ (0.94)	$ 0.62
Diluted (in dollars per share)	$ (0.44)	$ 1.18	$ (0.94)	$ 0.61

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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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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