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Earnings Per Share - Earnings Per Share Reconciliation (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Earnings Per Share [Abstract]                      
Net income per basic common share, Net Income (Numerator) $ 185,152 $ 141,014 $ 155,677 $ 111,951 $ (353,172) $ 136,104 $ 131,822 $ 105,557 $ 593,794 $ 20,311 $ 521,503
Net income per diluted common share, Net Income (Numerator)                 $ 593,794 $ 20,311 $ 521,503
Net income per basic common share, Weighted-Average Shares (Denominator) 74,802 76,575 77,833 78,883 79,454 79,712 79,979 80,073 76,992 79,793 80,786
Effect of dilutive stock option, restricted stock, performance stock unit and restricted stock unit securities, Weighted-Average Shares (Denominator)                 626 811 631
Net income per diluted common share, Weighted-Average Shares (Denominator) 75,345 77,136 78,438 79,715 79,454 80,521 80,756 80,769 77,618 80,604 81,417
Net income per basic common share, Per Share Amount $ 2.48 $ 1.84 $ 2.00 $ 1.42 $ (4.44) $ 1.71 $ 1.65 $ 1.32 $ 7.71 $ 0.25 $ 6.46
Effect of dilutive stock option, restricted stock, performance stock unit and restricted stock unit securities, Per Share Amount                 (0.06)   (0.05)
Net income per diluted common share, Per Share Amount $ 2.46 $ 1.83 $ 1.98 $ 1.40 $ (4.44) $ 1.69 $ 1.63 $ 1.31 $ 7.65 $ 0.25 $ 6.41