Investment Information - Allowance for expected credit losses (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Allowance for expected credit losses
Balance at beginning of period		$ 2,397	$ 0	$ 0
Cumulative effect of accounting change	[1]			634
Additions for current-period provision for expected credit losses		2,603		10,653
Additions (reductions) for previously recognized expected credit losses		(931)		(7,030)
Reductions due to disposals		(239)		(1,860)
Write-offs charged against the allowance		0		0
Balance at end of period		$ 3,830		2,397
Accounting Standards Update		us-gaap:AccountingStandardsUpdate201613Member
Fixed maturities
Allowance for expected credit losses
Balance at beginning of period		$ 2,397
Additions for current-period provision for expected credit losses		1,648	9,320
Balance at end of period		3,830		2,397
Fixed maturities | Structured securities
Allowance for expected credit losses
Balance at beginning of period	[2]	1,490	0	0
Cumulative effect of accounting change	[1],[2]			517
Additions for current-period provision for expected credit losses	[2]	182		2,942
Additions (reductions) for previously recognized expected credit losses	[2]	(382)		(1,398)
Reductions due to disposals	[2]	(83)		(571)
Write-offs charged against the allowance	[2]	0		0
Balance at end of period		1,207		1,490	[2]
Fixed maturities | Municipal bonds
Allowance for expected credit losses
Balance at beginning of period		11	0	0
Cumulative effect of accounting change	[1]			0
Additions for current-period provision for expected credit losses		0		67
Additions (reductions) for previously recognized expected credit losses		(9)		6
Reductions due to disposals		0		(62)
Write-offs charged against the allowance		0		0
Balance at end of period		2		11
Fixed maturities | Corporate bonds
Allowance for expected credit losses
Balance at beginning of period		896	$ 0	0
Cumulative effect of accounting change	[1]			117
Additions for current-period provision for expected credit losses		2,421		7,644
Additions (reductions) for previously recognized expected credit losses		(540)		(5,638)
Reductions due to disposals		(156)		(1,227)
Write-offs charged against the allowance		0		0
Balance at end of period		$ 2,621		$ 896

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

[2] Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities.