Investments - Unrealized gains and losses (Details) - Municipal bonds - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Net Investment Income [Line Items]
Unrealized Gains	$ 1,007	$ 1,219
Unrealized Losses	$ 0	$ 0

The increase (decrease), resulting in a gain, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

No definition available.

Name:	us-gaap_UnrealizedGainOnSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration