Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fixed maturities [Abstract]
Total fixed maturities	$ 576,388	$ 521,853
Equity securities [Abstract]
Total equity securities	125,407	201,763
Recurring [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	14,961	16,586
Agency mortgage-backed securities	33,708	27,075
Asset-backed securities	51,454	43,469
Bank loans	20,202	19,488
Certificates of deposit	3,122	3,135
Collateralized mortgage obligations	5,135	6,492
Corporate securities	206,291	193,058
Options embedded in convertible securities	5,768	5,291
Mortgage-backed securities	30,954	24,204
Municipal obligations	48,327	96,650
Non-U.S. government obligations	38,602	37,394
U.S. government obligations	117,864	49,011
Total fixed maturities	576,388	521,853
Equity securities [Abstract]
Consumer	25,000	46,578
Energy	7,240	10,278
Financial	37,243	45,470
Industrial	13,144	25,402
Technology	4,129	13,061
Funds (e.g. mutual funds, closed end funds, ETFs)	27,908	50,291
Other	10,743	10,683
Total equity securities	125,407	201,763
Short-term	1,000	1,000
Cash equivalents	73,600	59,173
Total fair value	776,395	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	3,122	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	3,122	3,135
Equity securities [Abstract]
Consumer	25,000	46,578
Energy	7,240	10,278
Financial	37,243	45,470
Industrial	13,144	25,402
Technology	4,129	13,061
Funds (e.g. mutual funds, closed end funds, ETFs)	22,873	45,276
Other	10,743	10,683
Total equity securities	120,372	196,748
Short-term	1,000	1,000
Cash equivalents	0	0
Total fair value	124,494	200,883
Recurring [Member] | Level 2 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	14,961	16,586
Agency mortgage-backed securities	33,708	27,075
Asset-backed securities	51,454	43,469
Bank loans	20,202	19,488
Certificates of deposit	0	0
Collateralized mortgage obligations	5,135	6,492
Corporate securities	206,291	193,058
Options embedded in convertible securities	5,768	5,291
Mortgage-backed securities	30,954	24,204
Municipal obligations	48,327	96,650
Non-U.S. government obligations	38,602	37,394
U.S. government obligations	117,864	49,011
Total fixed maturities	573,266	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)	5,035	5,015
Other	0	0
Total equity securities	5,035	5,015
Short-term	0	0
Cash equivalents	73,600	59,173
Total fair value	651,901	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