Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of the component parts of earnings per share [Abstract]
Net income	$ 15,199	$ 12,596	$ 45,412	$ 35,783
Weighted average common shares (in shares)	96,555	96,102	96,453	95,997
Effect of dilutive common stock options (in shares)	134	103	134	94
Weighted average common shares including potential dilutive shares (in shares)	96,689	96,205	96,587	96,091
Basic EPS (in dollars per share)	$ 0.157	$ 0.131	$ 0.471	$ 0.373
Diluted EPS (in dollars per share)	$ 0.157	$ 0.131	$ 0.470	$ 0.372
Stock Options [Member]
Antidilutive Securities [Abstract]
Weighted average number of antidilutive stock options excluded from diluted earnings per share (in shares)	0	995	0	1,400

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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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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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