Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated Other Comprehensive Income (Loss)	Unrealized investment gain	Currency Translation Adjustments	Treasury stock	Noncontrolling interest
Beginning of period at Dec. 31, 2016		$ 47,024	$ 1,037,446	$ 6,595,987	$ 55,568	$ 427,154	$ (371,586)	$ (2,688,817)	$ 33,926
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(27,047)
Restricted stock units expensed			30,176
Cumulative effect adjustment resulting from changes in accounting principles				0		0
Net income before noncontrolling interests	$ 397,065			394,505					2,560
Dividends				(110,430)
Change in unrealized (losses) gains on securities not other-than-temporarily impaired	26,598					25,712
Change in unrealized gains on other-than-temporarily impaired securities						905
Net change in period	71,574						71,574
Stock exercised/vested								25,584
Stock repurchased								(28,378)
Stock issued								727
(Distributions) contributions									3,646
Other comprehensive income (loss), net of tax	98,172				98,172		71,574		(19)
End of period at Sep. 30, 2017			1,040,575	6,880,062	153,759	453,771	(300,012)	(2,690,884)	40,113
Beginning of period at Jun. 30, 2017					133,302		(328,604)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income before noncontrolling interests	162,818
Change in unrealized (losses) gains on securities not other-than-temporarily impaired	(8,168)
Net change in period	28,592						28,592
Other comprehensive income (loss), net of tax	20,424				20,424		28,592
End of period at Sep. 30, 2017			1,040,575	6,880,062	153,759	453,771	(300,012)	(2,690,884)	40,113
Beginning of period at Dec. 31, 2017	5,451,163	$ 47,024	1,048,283	6,956,882	68,541	375,421	(306,880)	(2,709,386)	39,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(16,690)
Restricted stock units expensed			26,481
Cumulative effect adjustment resulting from changes in accounting principles				215,939		(214,539)
Net income before noncontrolling interests	512,794			508,392					4,402
Dividends				(175,507)
Change in unrealized (losses) gains on securities not other-than-temporarily impaired	(253,056)					(252,974)
Change in unrealized gains on other-than-temporarily impaired securities						4
Net change in period	(75,970)						(75,970)
Stock exercised/vested								17,478
Stock repurchased								(6,799)
Stock issued								689
(Distributions) contributions									(2,950)
Other comprehensive income (loss), net of tax	(329,026)				(329,026)		(75,970)		(86)
End of period at Sep. 30, 2018	5,479,033		1,058,074	7,505,706	(474,938)	(92,088)	(382,850)	(2,698,018)	41,185
Beginning of period at Jun. 30, 2018					(395,842)		(398,536)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income before noncontrolling interests	164,443
Change in unrealized (losses) gains on securities not other-than-temporarily impaired	(94,842)
Net change in period	15,686						15,686
Other comprehensive income (loss), net of tax	(79,156)				(79,156)		15,686
End of period at Sep. 30, 2018	$ 5,479,033		$ 1,058,074	$ 7,505,706	$ (474,938)	$ (92,088)	$ (382,850)	$ (2,698,018)	$ 41,185