Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 224,606	$ 188,167	$ 187,271	$ 109,804	$ 93,174	$ 151,461	$ 155,091	$ 76,172	$ 709,848	$ 475,898	$ 421,863
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on securities									125,283	(38,418)	63,563
Foreign currency translation adjustment									13,960	(26,796)	24,744
Pension benefit adjustment									(20,161)	12,680	74,597
Total other comprehensive income (loss), net of tax									119,082	(52,534)	162,904
Comprehensive income									828,930	423,364	584,767
Less: Comprehensive income (loss) attributable to noncontrolling interests									2,437	1,384	(1,173)
Comprehensive income attributable to the Company									$ 826,493	$ 421,980	$ 585,940