Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 107,392	$ 75,759	$ 262,515	$ 207,135
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on securities	2,579	(10,942)	52,087	(19,374)
Foreign currency translation adjustment	(3,459)	(15,416)	3,066	(29,210)
Pension benefit adjustment	3,602	4,058	10,819	13,260
Total other comprehensive income (loss), net of tax	2,722	(22,300)	65,972	(35,324)
Comprehensive income	110,114	53,459	328,487	171,811
Less: Comprehensive income attributable to noncontrolling interests	77	206	566	598
Comprehensive income attributable to the Company	$ 110,037	$ 53,253	$ 327,921	$ 171,213