Stockholders' Equity and EPS - Reconciliation of Basic EPS to Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income available to common stockholders	$ 267,281	$ 274,817	$ 874,000	$ 707,576
Denominator:
Weighted average common shares outstanding-basic (in shares)	51,545	53,235	52,025	53,062
Weighted average common shares outstanding—diluted (in shares)	51,858	53,919	52,431	53,800
Earnings per common share:
Basic (dollars per share)	$ 5.19	$ 5.16	$ 16.80	$ 13.33
Diluted (dollars per share)	$ 5.15	$ 5.10	$ 16.67	$ 13.15
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	203	383	238	404
Restricted stock units and awards
Denominator:
Weighted average effect of dilutive securities (in shares)	110	301	168	334

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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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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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