Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period			$ 5,451,163
Other comprehensive income (loss)	$ (79,156)	$ 20,424	(329,026)	$ 98,172
End of period	5,479,033		5,479,033
Net realized and unrealized gains on investments	22,334	183,959	140,429	276,760
Income before income taxes	209,223	226,113	649,455	571,370
Tax effect	(44,780)	(63,295)	(136,661)	(174,305)
Net income before noncontrolling interests	164,443	162,818	512,794	397,065
Net change in period	15,686	28,592	(75,970)	71,574
Other comprehensive income (loss), pre-tax	(81,142)	20,029	(374,134)	121,722
Other comprehensive income (loss), tax effect	1,986	395	45,108	(23,550)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(395,842)	133,302	68,541	55,568
Cumulative effect adjustment resulting from changes in accounting principles					$ (214,539)
Restated beginning of period					(145,998)
Other comprehensive income (loss) before reclassifications	(79,626)	48,560	(318,914)	180,851
Amounts reclassified from AOCI	470	(28,136)	(10,112)	(82,679)
Other comprehensive income (loss)	(79,156)	20,424	(329,026)	98,172
End of period	(474,938)	153,759	(474,938)	153,759
Unrealized investment gain related to noncontrolling interest	60	33	86	19
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income before income taxes	595	(43,286)	(12,800)	(127,198)
Tax effect	(125)	15,150	2,688	44,519
Net income before noncontrolling interests	470	(28,136)	(10,112)	(82,679)
Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	2,694	461,906	375,421	427,154
Cumulative effect adjustment resulting from changes in accounting principles					(214,539)
Restated beginning of period					160,882
Other comprehensive income (loss) before reclassifications	(95,312)	19,968	(242,944)	109,277
Amounts reclassified from AOCI	470	(28,136)	(10,112)	(82,679)
Other comprehensive income (loss)	(94,842)	(8,168)	(253,056)	26,598
End of period	(92,088)	453,771	(92,088)	453,771
Unrealized investment gain related to noncontrolling interest	60	33	86	19
Unrealized investment gains, pre-tax	(96,828)	(8,563)	(298,164)	50,148
Unrealized investment gains, tax effect	1,986	395	45,108	(23,550)
Unrealized investment gains (losses), after-tax amounts	(94,842)	(8,168)	(253,056)	26,598
Unrealized Investment Gains (Losses) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net realized and unrealized gains on investments	595	(43,286)	(12,800)	(127,198)
Tax effect	(125)	15,150	2,688	44,519
Net income before noncontrolling interests	470	(28,136)	(10,112)	(82,679)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(398,536)	(328,604)	(306,880)	(371,586)
Cumulative effect adjustment resulting from changes in accounting principles					0
Restated beginning of period					$ (306,880)
Other comprehensive income (loss) before reclassifications	15,686	28,592	(75,970)	71,574
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss)	15,686	28,592	(75,970)	71,574
End of period	(382,850)	(300,012)	(382,850)	(300,012)
Unrealized investment gain related to noncontrolling interest	0	0	0	0
Currency translation adjustment, pre-tax	15,686	28,592	(75,970)	71,574
Currency translation adjustment, tax effect	0	0	0	0
Net change in period	15,686	28,592	(75,970)	71,574
Currency Translation Adjustments | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income before income taxes	0	0	0	0
Tax effect	0	0	0	0
Net income before noncontrolling interests	$ 0	$ 0	$ 0	$ 0