Business Combinations - Unaudited Pro Forma Results (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Two Thousand Twenty Acquisition
Business Acquisition Pro Forma Information Nonrecurring Adjustment [Line Items]
Total revenues	$ 2,714,314	$ 2,579,075
Income before income taxes	650,618	576,355
Net income	$ 500,900	$ 436,722
Net income per share:
Basic	$ 1.77	$ 1.55
Diluted	$ 1.76	$ 1.54
Weighted average number of shares outstanding:
Basic	274,334	272,471
Diluted	275,867	274,616
Two Thousand Nineteen Acquisition
Business Acquisition Pro Forma Information Nonrecurring Adjustment [Line Items]
Total revenues		$ 2,447,401	$ 2,120,867
Income before income taxes		545,182	496,076
Net income		$ 412,974	$ 369,277
Net income per share:
Basic		$ 1.47	$ 1.33
Diluted		$ 1.46	$ 1.31
Weighted average number of shares outstanding:
Basic		272,471	270,971
Diluted		274,616	275,521
Two Thousand Eighteen Acquisition
Business Acquisition Pro Forma Information Nonrecurring Adjustment [Line Items]
Total revenues			$ 2,259,812	$ 2,193,169
Income before income taxes			504,664	503,927
Net income			$ 375,670	$ 447,796
Net income per share:
Basic			$ 1.35	$ 1.60
Diluted			$ 1.33	$ 1.57
Weighted average number of shares outstanding:
Basic			270,971	272,580
Diluted			275,521	277,586