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, 2017		$ 70,535	$ 1,024,771	$ 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			(5,642)
Restricted stock units expensed			17,667
Cumulative effect adjustment resulting from changes in accounting principles				215,939		(214,539)
Net income before noncontrolling interests	$ 348,351			346,472					1,879
Dividends ($0.61, $0.43, $0.71 and $0.53 per share, respectively)				(96,131)
Change in unrealized gains (losses) on securities not other-than-temporarily impaired	(158,214)					(158,199)
Change in unrealized gains (losses) on other-than-temporarily impaired securities						11
Net change in period	(91,656)						(91,656)
Stock exercised/vested								6,963
Stock repurchased								(6,799)
Stock issued								688
Distributions									(2,162)
Other comprehensive income (loss), net of tax	$ (249,870)				(249,870)		(91,656)		(26)
End of period at Jun. 30, 2018			1,036,796	7,423,162	(395,842)	2,694	(398,536)	(2,708,534)	39,510
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.53
Beginning of period at Mar. 31, 2018		70,535	1,033,718	7,322,201	(258,982)	35,099	(294,081)	(2,715,697)	40,404
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(5,155)
Restricted stock units expensed			8,233
Cumulative effect adjustment resulting from changes in accounting principles				0		0
Net income before noncontrolling interests	$ 180,778			180,075					703
Dividends ($0.61, $0.43, $0.71 and $0.53 per share, respectively)				(79,114)
Change in unrealized gains (losses) on securities not other-than-temporarily impaired	(32,442)					(32,403)
Change in unrealized gains (losses) on other-than-temporarily impaired securities						(2)
Net change in period	(104,455)						(104,455)
Stock exercised/vested								6,475
Stock repurchased								0
Stock issued								688
Distributions									(1,560)
Other comprehensive income (loss), net of tax	$ (136,897)				(136,897)		(104,455)		(37)
End of period at Jun. 30, 2018			1,036,796	7,423,162	(395,842)	2,694	(398,536)	(2,708,534)	39,510
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.43
Beginning of period at Dec. 31, 2018	$ 5,479,798	70,535	1,039,633	7,558,619	(510,470)	(91,491)	(418,979)	(2,720,466)	41,947
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(2,504)
Restricted stock units expensed			21,287
Cumulative effect adjustment resulting from changes in accounting principles				0		0
Net income before noncontrolling interests	399,041			397,431					1,610
Dividends ($0.61, $0.43, $0.71 and $0.53 per share, respectively)				(130,035)
Change in unrealized gains (losses) on securities not other-than-temporarily impaired	244,424					244,393
Change in unrealized gains (losses) on other-than-temporarily impaired securities						13
Net change in period	5,268						5,268
Stock exercised/vested								2,504
Stock repurchased								0
Stock issued								552
Distributions									(221)
Other comprehensive income (loss), net of tax	249,692				249,692		5,268		(18)
End of period at Jun. 30, 2019	$ 6,020,078		1,058,416	7,826,015	(260,796)	152,915	(413,711)	(2,717,410)	43,318
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.71
Beginning of period at Mar. 31, 2019		$ 70,535	1,053,372	7,721,039	(364,983)	34,236	(399,219)	(2,720,011)	42,844
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(2,049)
Restricted stock units expensed			7,093
Cumulative effect adjustment resulting from changes in accounting principles				0		0
Net income before noncontrolling interests	$ 217,427			216,709					718
Dividends ($0.61, $0.43, $0.71 and $0.53 per share, respectively)				(111,733)
Change in unrealized gains (losses) on securities not other-than-temporarily impaired	118,649					118,597
Change in unrealized gains (losses) on other-than-temporarily impaired securities						82
Net change in period	(14,492)						(14,492)
Stock exercised/vested								2,049
Stock repurchased								0
Stock issued								552
Distributions									(274)
Other comprehensive income (loss), net of tax	104,157				104,157		(14,492)		30
End of period at Jun. 30, 2019	$ 6,020,078		$ 1,058,416	$ 7,826,015	$ (260,796)	$ 152,915	$ (413,711)	$ (2,717,410)	$ 43,318
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.61