Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 21,186	$ 107,392	$ 201,150	$ 262,515
Other comprehensive income (loss), net of tax:
Unrealized gains on securities	13,929	2,579	52,014	52,087
Foreign currency translation adjustment	11,415	(3,459)	23,558	3,066
Pension benefit adjustment	85,891	3,602	93,061	10,819
Total other comprehensive income, net of tax	111,235	2,722	168,633	65,972
Comprehensive income	132,421	110,114	369,783	328,487
Less: Comprehensive (loss) income attributable to noncontrolling interests	(192)	77	(760)	566
Comprehensive income attributable to the Company	$ 132,613	$ 110,037	$ 370,543	$ 327,921