Consolidated Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ 6,118,342
Other comprehensive income (loss)	(357,175)	$ 145,534
End of period	5,537,544
Net realized and unrealized (losses) gains on investments	(143,285)	68,653
(Loss) income before income taxes	(6,468)	229,439
Tax effect	2,942	(47,825)
Net (loss) income before noncontrolling interests	(3,526)	181,614
Total change in unrealized investment (losses) gains	(332,850)	169,260
Net change in period	(98,194)	19,760
Other comprehensive income (loss), pre-tax	(431,044)	189,020
Other comprehensive income (loss), tax effect	73,869	(43,486)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(257,299)	(510,470)
Other comprehensive income (loss) before reclassifications	(396,725)	146,899
Amounts reclassified from AOCI	39,550	(1,365)
Other comprehensive income (loss)	(357,175)	145,534
End of period	(589,521)	(364,983)
Unrealized investment loss related to noncontrolling interest	1	(47)
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
(Loss) income before income taxes	50,063	(1,728)
Tax effect	(10,513)	363
Net (loss) income before noncontrolling interests	39,550	(1,365)
Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	124,514	(91,491)
Other comprehensive income (loss) before reclassifications	(298,531)	127,139
Amounts reclassified from AOCI	39,550	(1,365)
Other comprehensive income (loss)	(258,981)	125,774
End of period	(109,514)	34,236
Unrealized investment loss related to noncontrolling interest	1	(47)
Total change in unrealized investment (losses) gains	(332,850)	169,260
Unrealized investment gains, tax effect	73,869	(43,486)
Unrealized investment gains (losses), after-tax amounts	(258,981)	125,774
Unrealized Investment Gains (Losses) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net realized and unrealized (losses) gains on investments	50,063	(1,728)
Tax effect	(10,513)	363
Net (loss) income before noncontrolling interests	39,550	(1,365)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(381,813)	(418,979)
Other comprehensive income (loss) before reclassifications	(98,194)	19,760
Amounts reclassified from AOCI	0	0
Other comprehensive income (loss)	(98,194)	19,760
End of period	(480,007)	(399,219)
Unrealized investment loss related to noncontrolling interest	0	0
Currency translation adjustment, pre-tax	(98,194)	19,760
Currency translation adjustment, tax effect	0	0
Net change in period	(98,194)	19,760
Currency Translation Adjustments | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
(Loss) income before income taxes	0	0
Tax effect	0	0
Net (loss) income before noncontrolling interests	0	$ 0
Cumulative effect adjustment resulting from changes in accounting principles | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	24,952
Cumulative effect adjustment resulting from changes in accounting principles | Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	24,952
Cumulative effect adjustment resulting from changes in accounting principles | Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	0
Cumulative Effect, Period Of Adoption, Adjusted Balance | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(232,347)
Cumulative Effect, Period Of Adoption, Adjusted Balance | Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	149,466
Cumulative Effect, Period Of Adoption, Adjusted Balance | Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ (381,813)