Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fixed maturities [Abstract]
Total fixed maturities	$ 544,116	$ 521,853
Equity securities [Abstract]
Total equity securities	149,027	201,763
Recurring [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	14,995	16,586
Agency mortgage-backed securities	30,740	27,075
Asset-backed securities	44,740	43,469
Bank loans	22,693	19,488
Certificates of deposit	3,127	3,135
Collateralized mortgage obligations	5,727	6,492
Corporate securities	208,270	193,058
Options embedded in convertible securities	5,192	5,291
Mortgage-backed securities	23,620	24,204
Municipal obligations	48,764	96,650
Non-U.S. government obligations	38,848	37,394
U.S. government obligations	97,400	49,011
Total fixed maturities	544,116	521,853
Equity securities [Abstract]
Consumer	27,519	46,578
Energy	6,636	10,278
Financial	47,771	45,470
Industrial	11,671	25,402
Technology	8,203	13,061
Funds (e.g. mutual funds, closed end funds, ETFs)	37,375	50,291
Other	9,852	10,683
Total equity securities	149,027	201,763
Short-term	1,000	1,000
Cash equivalents	76,639	59,173
Total fair value	770,782	783,789
Recurring [Member] | Level 1 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	0	0
Agency mortgage-backed securities	0	0
Asset-backed securities	0	0
Bank loans	0	0
Certificates of deposit	3,127	3,135
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 fixed maturities	3,127	3,135
Equity securities [Abstract]
Consumer	27,519	46,578
Energy	6,636	10,278
Financial	47,771	45,470
Industrial	11,671	25,402
Technology	8,203	13,061
Funds (e.g. mutual funds, closed end funds, ETFs)	32,364	45,276
Other	9,852	10,683
Total equity securities	144,016	196,748
Short-term	1,000	1,000
Cash equivalents	0	0
Total fair value	148,143	200,883
Recurring [Member] | Level 2 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	14,995	16,586
Agency mortgage-backed securities	30,740	27,075
Asset-backed securities	44,740	43,469
Bank loans	22,693	19,488
Certificates of deposit	0	0
Collateralized mortgage obligations	5,727	6,492
Corporate securities	208,270	193,058
Options embedded in convertible securities	5,192	5,291
Mortgage-backed securities	23,620	24,204
Municipal obligations	48,764	96,650
Non-U.S. government obligations	38,848	37,394
U.S. government obligations	97,400	49,011
Total fixed maturities	540,989	518,718
Equity securities [Abstract]
Consumer	0	0
Energy	0	0
Financial	0	0
Industrial	0	0
Technology	0	0
Funds (e.g. mutual funds, closed end funds, ETFs)	5,011	5,015
Other	0	0
Total equity securities	5,011	5,015
Short-term	0	0
Cash equivalents	76,639	59,173
Total fair value	622,639	582,906
Recurring [Member] | Level 3 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	0	0
Agency mortgage-backed securities	0	0
Asset-backed securities	0	0
Bank loans	0	0
Certificates of deposit	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 fixed maturities	0	0
Equity securities [Abstract]
Consumer	0	0
Energy	0	0
Financial	0	0
Industrial	0	0
Technology	0	0
Funds (e.g. mutual funds, closed end funds, ETFs)	0	0
Other	0	0
Total equity securities	0	0
Short-term	0	0
Cash equivalents	0	0
Total fair value	$ 0	$ 0