Deferred Acquisition Costs (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement Analysis of Deferred Policy Acquisition Costs
Balance at beginning of year				$ 4,341,941				$ 4,137,925	$ 4,341,941	$ 4,137,925	$ 3,958,063
Deferred during period:
Commissions									600,577	534,735	497,459
Other expenses									222,408	218,926	202,092
Total deferred									822,985	753,661	699,551
Foreign exchange adjustment									4,755	4,299	0
Adjustment attributable to unrealized investment losses									1,533	0	5,549
Total additions									829,273	757,960	705,100
Amortized during period	$ (144,930)	$ (140,843)	$ (146,160)	$ (143,837)	$ (139,290)	$ (138,449)	$ (138,165)	$ (135,822)	(575,770)	(551,726)	(516,690)
Foreign exchange adjustment									0	0	(8,548)
Adjustment attributable to unrealized investment gains									0	(2,218)	0
Total deductions									(575,770)	(553,944)	(525,238)
Balance at end of year	$ 4,595,444				$ 4,341,941				$ 4,595,444	$ 4,341,941	$ 4,137,925