Allowance for expected credit losses - Reinsurance recoverable (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)		Jun. 30, 2020 USD ($)
Credit Loss [Abstract]
Balance at beginning of period	$ 197,458		$ 170,974
Balance at end of period	229,746		229,746
Deferred tax asset	22		22
Reinsurance Recoverable, Allowance for Credit Loss
Balance at beginning of period	297		0
Cumulative effect of adoption of updated accounting guidance for credit losses at January 1, 2020	0	[1]	297	[1]
Current period change for expected credit losses	(16)		(16)
Write-offs charged against the allowance	0		0
Balance at end of period	$ 281		$ 281

[1] the allowance for credit losses is gross of deferred tax of $22 thousand.