Earnings per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 4,357	$ 11,778	$ 17,207	$ 22,634
Net income allocated to unvested restricted stock	(33)	(122)	(132)	(234)
Net income allocated to common shares	$ 4,324	$ 11,656	$ 17,075	$ 22,400
Weighted average shares outstanding	29,404	26,661	29,380	26,647
Average unvested restricted stock	(228)	(281)	(221)	(284)
Denominator for basic earnings per share—weighted-average shares outstanding	29,176	26,380	29,159	26,363
Effect of dilutive securities—employee stock options	95	97	95	100
Denominator for diluted earnings per share—adjusted weighted-average shares outstanding	29,271	26,477	29,254	26,463
Basic earnings per share	$ 0.15	$ 0.44	$ 0.59	$ 0.85
Diluted earnings per share	$ 0.15	$ 0.44	$ 0.58	$ 0.85
Average anti-dilutive options excluded from computation of diluted earnings per share	369	188	294	157

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent, and includes adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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