CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 81,736	$ 75,759	$ 93,579	$ 37,796	$ 80,738	$ 80,937	$ 50,688	$ 21,852	$ 288,870	$ 234,215	$ 187,064
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains on securities									(27,312)	19,638	(30,665)
Foreign currency translation adjustment									(36,822)	(16,694)	(13,650)
Pension benefit adjustment									24,223	(56,496)	49,324
Total other comprehensive income (loss), net of tax									(39,911)	(53,552)	5,009
Comprehensive income									248,959	180,663	192,073
Less: Comprehensive income attributable to noncontrolling interests									770	691	694
Comprehensive income attributable to the Company									$ 248,189	$ 179,972	$ 191,379