Investment Information - Allowance for expected credit losses (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Allowance for expected credit losses
Balance at beginning of period		$ 9,938		$ 0
Cumulative effect of accounting change		0		634
Additions for current-period provision for expected credit losses		1,000		10,349
Additions (reductions) for previously recognized expected credit losses		(4,232)		(4,255)
Reductions due to disposals		(837)		(859)
Write-offs charged against the allowance		0		0
Balance at end of period		5,869		5,869
Fixed maturities
Allowance for expected credit losses
Balance at beginning of period				0
Additions for current-period provision for expected credit losses		(3,225)	$ 0	6,095	$ 0
Balance at end of period		5,869		5,869
Fixed maturities | Structured securities
Allowance for expected credit losses
Balance at beginning of period		2,654		0
Cumulative effect of accounting change		0		517
Additions for current-period provision for expected credit losses		695		2,841
Additions (reductions) for previously recognized expected credit losses		(1,304)		(1,306)
Reductions due to disposals		(319)		(326)
Write-offs charged against the allowance		0		0
Balance at end of period		1,726		1,726
Fixed maturities | Municipal bonds
Allowance for expected credit losses
Balance at beginning of period		23		0
Cumulative effect of accounting change		0		0
Additions for current-period provision for expected credit losses		44		67
Additions (reductions) for previously recognized expected credit losses		(25)		(25)
Reductions due to disposals		(14)		(14)
Write-offs charged against the allowance		0		0
Balance at end of period		28		28
Fixed maturities | Corporate bonds
Allowance for expected credit losses
Balance at beginning of period		7,232		0
Cumulative effect of accounting change		0		117
Additions for current-period provision for expected credit losses		290		7,441
Additions (reductions) for previously recognized expected credit losses		(2,903)		(2,924)
Reductions due to disposals		(504)		(519)
Write-offs charged against the allowance		0		0
Balance at end of period		4,115		4,115
Short-term investments
Allowance for expected credit losses
Balance at beginning of period		29		0
Cumulative effect of accounting change		0		0
Additions for current-period provision for expected credit losses		(29)		0
Additions (reductions) for previously recognized expected credit losses		0		0
Reductions due to disposals		0		0
Write-offs charged against the allowance		0		0
Balance at end of period	[1]	$ 0		$ 0

[1] Effective January 1, 2020, the Company adopted ASU 2016-13 and as a result any credit impairment losses on the Company’s available-for-sale investments are recorded as an allowance, subject to reversal.