Consolidated Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	$ 5,479,798
Other comprehensive gain (loss)	253,068	$ (364,426)	$ 12,954
End of period	6,118,342	5,479,798
Net investment gains	120,703	154,488	335,858
Federal and foreign income taxes	(168,935)	(163,028)	(219,433)
Net income before noncontrolling interests	683,985	649,066	553,337
Unrealized investment gains, before tax	261,970	(302,737)	(69,425)
Currency translation adjustments, before tax	37,166	(112,099)
Other comprehensive income (loss), before tax	299,136	(414,836)
Unrealized investment gains, tax	(46,068)	50,410
Currency translation adjustments, tax	0	0
Other comprehensive income (loss), tax	(46,068)	50,410
Unrealized investment gains, net of tax	215,902	(252,327)
Change in unrealized translation adjustments	37,166	(112,099)	64,706
Unrealized investment gains (losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	(91,491)	375,421
Cumulative effect adjustment resulting from changes in accounting principles				$ (214,539)
Restated beginning of period				160,882
Other comprehensive gains before reclassifications	224,011	(246,535)
Amounts reclassified from AOCI	(8,109)	(5,792)
Other comprehensive gain (loss)	215,902	(252,327)
Unrealized investment gain related to non-controlling interest	103	(46)
End of period	124,514	(91,491)	375,421
Unrealized investment gains (losses) | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gains	(10,265)	(7,332)
Federal and foreign income taxes	2,156	1,540
Net income before noncontrolling interests	(8,109)	(5,792)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	(418,979)	(306,880)	(371,586)
Cumulative effect adjustment resulting from changes in accounting principles				0
Restated beginning of period				(306,880)
Other comprehensive gains before reclassifications	37,166	(112,099)
Amounts reclassified from AOCI	0	0
Other comprehensive gain (loss)	37,166	(112,099)
Unrealized investment gain related to non-controlling interest	0	0
End of period	(381,813)	(418,979)	(306,880)
Change in unrealized translation adjustments	37,166	(112,099)	64,706
Currency translation adjustments | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gains	0	0
Federal and foreign income taxes	0	0
Net income before noncontrolling interests	0	0
Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	(510,470)	68,541
Cumulative effect adjustment resulting from changes in accounting principles				(214,539)
Restated beginning of period				$ (145,998)
Other comprehensive gains before reclassifications	261,177	(358,634)
Amounts reclassified from AOCI	(8,109)	(5,792)
Other comprehensive gain (loss)	253,068	(364,426)
Unrealized investment gain related to non-controlling interest	103	(46)
End of period	(257,299)	(510,470)	$ 68,541
Accumulated other comprehensive (loss) income | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gains	(10,265)	(7,332)
Federal and foreign income taxes	2,156	1,540
Net income before noncontrolling interests	$ (8,109)	$ (5,792)