Allowance for Expected Credit Losses - Contractholder receivables (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Credit Loss [Abstract]
Balance at beginning of period		$ 1,919,655	$ 2,140,724	$ 1,986,924	$ 2,119,460
Balance at end of period		1,882,948	2,179,124	1,882,948	2,179,124
Allowance for Expected Credit Losses
Balance at beginning of period		5,853	9,038	8,638	0
Cumulative effect of accounting change	[1]				6,663
Change for provision of expected credit losses		(1,382)	(2,748)	(4,167)	(373)
Balance at end of period		$ 4,471	$ 6,290	$ 4,471	$ 6,290

[1] Adoption of ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326)”