Schedule II - Condensed Statements Of Comprehensive Income Parent Company (Detail) - USD ($) $ 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
Condensed Statement Of Income Captions [Line Items]
Net income	$ 93,174	$ 151,461	$ 155,091	$ 76,172	$ 220,713	$ 21,186	$ 121,895	$ 58,069	$ 475,898	$ 421,863	$ 343,476
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains on securities									(38,418)	63,563	(10,359)
Foreign currency translation adjustment									(26,796)	24,744	(6,334)
Pension benefit adjustment									12,680	74,597	25,300
Total other comprehensive (loss) income, net of tax									(52,534)	162,904	8,607
Comprehensive income									423,364	584,767	352,083
Less: Comprehensive income (loss) attributable to noncontrolling interests									1,384	(1,173)	487
Comprehensive income attributable to the Company									421,980	585,940	351,596
Parent Company
Condensed Statement Of Income Captions [Line Items]
Net income									475,898	421,863	343,476
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains on securities									(38,418)	63,563	(10,359)
Foreign currency translation adjustment									(26,796)	24,744	(6,334)
Pension benefit adjustment									12,680	74,597	25,300
Total other comprehensive (loss) income, net of tax									(52,534)	162,904	8,607
Comprehensive income									423,364	584,767	352,083
Less: Comprehensive income (loss) attributable to noncontrolling interests									1,384	(1,173)	487
Comprehensive income attributable to the Company									$ 421,980	$ 585,940	$ 351,596