Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period				$ 5,479,798
Other comprehensive income (loss)		$ 104,157	$ (136,897)	249,692	$ (249,870)
End of period		6,020,078		6,020,078
Net realized and unrealized gains on investments		73,574	69,631	142,226	118,095
Income before income taxes		273,736	229,242	503,175	440,232
Tax effect		(56,309)	(48,464)	(104,134)	(91,881)
Net income before noncontrolling interests		217,427	180,778	399,041	348,351
Total change in unrealized investment gains (losses)		147,071	(40,488)	316,331	(201,336)
Net change in period		(14,492)	(104,455)	5,268	(91,656)
Other comprehensive income (loss), pre-tax		132,580	(144,943)	321,599	(292,992)
Other comprehensive income (loss), tax effect		(28,423)	8,046	(71,907)	43,122
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ 68,541	(364,983)	(258,982)	(510,470)	68,541
Cumulative effect adjustment resulting from changes in accounting principles	(214,539)
Restated beginning of period	(145,998)
Other comprehensive income (loss) before reclassifications		103,983	(133,898)	250,883	(239,288)
Amounts reclassified from AOCI		174	(2,999)	(1,191)	(10,582)
Other comprehensive income (loss)		104,157	(136,897)	249,692	(249,870)
End of period		(260,796)	(395,842)	(260,796)	(395,842)
Unrealized investment loss related to noncontrolling interest		30	37	(18)	26
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income before income taxes		220	(3,796)	(1,508)	(13,395)
Tax effect		(46)	797	317	2,813
Net income before noncontrolling interests		174	(2,999)	(1,191)	(10,582)
Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	375,421	34,236	35,099	(91,491)	375,421
Cumulative effect adjustment resulting from changes in accounting principles	(214,539)
Restated beginning of period	160,882
Other comprehensive income (loss) before reclassifications		118,475	(29,443)	245,615	(147,632)
Amounts reclassified from AOCI		174	(2,999)	(1,191)	(10,582)
Other comprehensive income (loss)		118,649	(32,442)	244,424	(158,214)
End of period		152,915	2,694	152,915	2,694
Unrealized investment loss related to noncontrolling interest		30	37	(18)	26
Total change in unrealized investment gains (losses)		147,072	(40,488)	316,331	(201,336)
Unrealized investment gains, tax effect		(28,423)	8,046	(71,907)	43,122
Unrealized investment gains (losses), after-tax amounts		118,649	(32,442)	244,424	(158,214)
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		220	(3,796)	(1,508)	(13,395)
Tax effect		(46)	797	317	2,813
Net income before noncontrolling interests		174	(2,999)	(1,191)	(10,582)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(306,880)	(399,219)	(294,081)	(418,979)	(306,880)
Cumulative effect adjustment resulting from changes in accounting principles	0
Restated beginning of period	$ (306,880)
Other comprehensive income (loss) before reclassifications		(14,492)	(104,455)	5,268	(91,656)
Amounts reclassified from AOCI		0	0	0	0
Other comprehensive income (loss)		(14,492)	(104,455)	5,268	(91,656)
End of period		(413,711)	(398,536)	(413,711)	(398,536)
Unrealized investment loss related to noncontrolling interest		0	0	0	0
Currency translation adjustment, pre-tax		(14,492)	(104,455)	5,268	(91,656)
Currency translation adjustment, tax effect		0	0	0	0
Net change in period		(14,492)	(104,455)	5,268	(91,656)
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