Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fixed income securities [Abstract]
Total, Fair Value	$ 914,949	$ 919,692
Equity securities [Abstract]
Total equity securities	67,015	58,169
Recurring [Member]
Fixed income securities [Abstract]
Agency collateralized mortgage obligations	11,821	11,931
Agency mortgage-backed securities	114,822	102,107
Asset-backed securities	102,638	107,696
Bank loans	12,073	11,361
Collateralized mortgage obligations	6,167	5,118
Corporate securities	351,511	352,837
Options embedded in convertible securities	10,931	7,404
Mortgage-backed securities	38,612	38,056
Municipal obligations	46,464	45,143
Non-U.S. government obligations	30,648	30,600
U.S. government obligations	189,262	207,439
Total, Fair Value	914,949	919,692
Equity securities [Abstract]
Consumer	12,373	11,598
Energy	1,661	1,227
Financial	34,108	29,064
Industrial	5,978	5,180
Technology	3,669	2,851
Other	9,226	8,249
Total equity securities	67,015	58,169
Short-term investments	1,000	1,000
Cash equivalents	86,961	47,026
Total	1,069,925	1,025,887
Recurring [Member] | Level 1 [Member]
Fixed income securities [Abstract]
Agency collateralized mortgage obligations	0	0
Agency mortgage-backed securities	0	0
Asset-backed securities	0	0
Bank loans	0	0
Collateralized mortgage obligations	0	0
Corporate securities	0	0
Options embedded in convertible securities	0	0
Mortgage-backed securities	0	0
Municipal obligations	0	0
Non-U.S. government obligations	0	0
U.S. government obligations	0	0
Total, Fair Value	0	0
Equity securities [Abstract]
Consumer	12,373	11,598
Energy	1,661	1,227
Financial	34,108	29,064
Industrial	5,978	5,180
Technology	3,669	2,851
Other	9,226	8,249
Total equity securities	67,015	58,169
Short-term investments	1,000	1,000
Cash equivalents	0	0
Total	68,015	59,169
Recurring [Member] | Level 2 [Member]
Fixed income securities [Abstract]
Agency collateralized mortgage obligations	11,821	11,931
Agency mortgage-backed securities	114,822	102,107
Asset-backed securities	102,638	107,696
Bank loans	12,073	11,361
Collateralized mortgage obligations	6,167	5,118
Corporate securities	351,511	352,837
Options embedded in convertible securities	10,931	7,404
Mortgage-backed securities	38,612	38,056
Municipal obligations	46,464	45,143
Non-U.S. government obligations	30,648	30,600
U.S. government obligations	189,262	207,439
Total, Fair Value	914,949	919,692
Equity securities [Abstract]
Consumer	0	0
Energy	0	0
Financial	0	0
Industrial	0	0
Technology	0	0
Other	0	0
Total equity securities	0	0
Short-term investments	0	0
Cash equivalents	86,961	47,026
Total	1,001,910	966,718
Recurring [Member] | Level 3 [Member]
Fixed income securities [Abstract]
Agency collateralized mortgage obligations	0	0
Agency mortgage-backed securities	0	0
Asset-backed securities	0	0
Bank loans	0	0
Collateralized mortgage obligations	0	0
Corporate securities	0	0
Options embedded in convertible securities	0	0
Mortgage-backed securities	0	0
Municipal obligations	0	0
Non-U.S. government obligations	0	0
U.S. government obligations	0	0
Total, Fair Value	0	0
Equity securities [Abstract]
Consumer	0	0
Energy	0	0
Financial	0	0
Industrial	0	0
Technology	0	0
Other	0	0
Total equity securities	0	0
Short-term investments	0	0
Cash equivalents	0	0
Total	$ 0	$ 0