Nature of Business and Significant Accounting Policies (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator for earnings per share:
Net earnings for basic and diluted earnings per share	$ 282,425	$ 107,223	$ 166,626
Denominator for earnings per share:
Weighted average number of common shares outstanding	137,815	137,456	137,138
Assumed exercise of stock options and vesting of restricted stock awards, net of shares assumed reacquired under the treasury stock method	2,394	2,190	1,359
Diluted shares outstanding	140,209	139,646	138,497

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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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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

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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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