Earnings Per Share - Calculation of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic earnings per share:
Net income	$ 542,156	$ 789,976	$ 720,196	$ 709,067	$ 586,970	$ 665,244	$ 270,650	$ 344,052	$ 2,761,395	$ 1,866,916	$ 1,211,242
Weighted-average common shares outstanding (in shares)									440,922	437,799	435,374
Basic earnings per share (in USD per share)	$ 1.23	$ 1.79	$ 1.63	$ 1.61	$ 1.34	$ 1.52	$ 0.62	$ 0.79	$ 6.26	$ 4.26	$ 2.78
Diluted earnings per share:
Net income	$ 542,156	$ 789,976	$ 720,196	$ 709,067	$ 586,970	$ 665,244	$ 270,650	$ 344,052	$ 2,761,395	$ 1,866,916	$ 1,211,242
Shares used in computation:
Weighted-average common shares outstanding (in shares)									440,922	437,799	435,374
Employee stock options (in shares)									13,286	13,966	15,870
Weighted-average number of shares (in shares)									454,208	451,765	451,244
Diluted earnings per share (in USD per share)	$ 1.19	$ 1.74	$ 1.59	$ 1.57	$ 1.30	$ 1.47	$ 0.60	$ 0.76	$ 6.08	$ 4.13	$ 2.68