Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 109,804	$ 76,172
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on debt securities	59,505	(46,796)
Foreign currency translation adjustment	6,888	(3,752)
Pension benefit adjustment	(76)	120
Total other comprehensive income (loss), net of tax	66,317	(50,428)
Comprehensive income	176,121	25,744
Less: Comprehensive income (loss) attributable to noncontrolling interests	228	(74)
Comprehensive income attributable to the Company	$ 175,893	$ 25,818