Segment Information - Intersegment Activity Eliminated in Arriving at Consolidated Totals was Included in "All Other" Category (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 5,632,187	$ 5,295,883	$ 4,667,624
Income taxes (benefit)	915,556	743,284	595,025
Net income (loss)	1,408,306	1,315,114	1,079,667
Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Revenues	(43,941)	(48,625)	(48,972)
Expenses	(32,623)	(40,422)	(13,332)
Income taxes (benefit)	(4,606)	(3,338)	(14,503)
Net income (loss)	$ (6,712)	$ (4,865)	$ (21,137)