Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stocks	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Income	Unrealized Investment gains (losses)	Currency translation adjustments	Treasury Stock	Noncontrolling Interests
Beginning of period at Dec. 31, 2014		$ 47,024	$ 991,512	$ 5,732,410		$ 306,199	$ (122,649)	$ (2,364,551)	$ 34,189
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(16,748)
Restricted stock units expensed			30,691
Stock issued								623
Net income (loss)	$ 504,107			503,694					413
Dividends				(58,034)
Unrealized (losses) gains on securities not other-than-temporarily impaired	(125,542)					(125,391)
Unrealized gains (losses) on other-than-temporarily impaired securities						(113)
Net change in period	(124,744)						(124,744)
Stock exercised/vested								23,975
Stock repurchased								(223,652)
Contributions (distributions)									(1,602)
Other comprehensive income (loss), net of tax	(250,286)								(38)
End of period at Dec. 31, 2015		47,024	1,005,455	6,178,070	$ (66,698)	180,695	(247,393)	(2,563,605)	32,962
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(3,594)
Restricted stock units expensed			35,585
Stock issued								685
Net income (loss)	603,485			601,916					1,569
Dividends				(183,999)
Unrealized (losses) gains on securities not other-than-temporarily impaired	246,518					246,872
Unrealized gains (losses) on other-than-temporarily impaired securities						(413)
Net change in period	(124,193)						(124,193)
Stock exercised/vested								6,495
Stock repurchased								(132,392)
Contributions (distributions)									(546)
Other comprehensive income (loss), net of tax	122,325				122,325		(124,193)		(59)
End of period at Dec. 31, 2016	5,081,134	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			(27,959)
Restricted stock units expensed			38,796
Stock issued								727
Net income (loss)	553,337			549,094					4,243
Dividends				(188,199)
Unrealized (losses) gains on securities not other-than-temporarily impaired	(51,752)					(52,628)
Unrealized gains (losses) on other-than-temporarily impaired securities						895
Net change in period	64,706						64,706
Stock exercised/vested								26,511
Stock repurchased								(47,807)
Contributions (distributions)									1,631
Other comprehensive income (loss), net of tax	12,954				12,954		64,706		19
End 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