Net Income per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 76,289	$ 49,991
Less distributed and undistributed earnings allocated to participating securities	1,031	585
Net Income (Loss) Available to Common Stockholders, Basic	$ 75,258	$ 49,406
Weighted average common shares outstanding basic (in shares)	40,508	41,224
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	142	493
Weighted Average Number of Shares Outstanding, Diluted	40,650	41,717

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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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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class 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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