Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fixed maturities [Abstract]
Total fixed maturities	$ 521,853	$ 491,904
Equity securities [Abstract]
Total equity securities	201,763	119,945
Recurring [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	16,586	6,171
Agency mortgage-backed securities	27,075	4,770
Asset-backed securities	43,469	45,183
Bank loans	19,488	10,349
Certificates of deposit	3,135	3,117
Collateralized mortgage obligations	6,492	9,104
Corporate securities	193,058	137,932
Options embedded in convertible securities	5,291	4,751
Mortgage-backed securities	24,204	24,571
Municipal obligations	96,650	129,335
Non-U.S. government obligations	37,394	24,681
U.S. government obligations	49,011	91,940
Total fixed maturities	521,853	491,904
Equity securities [Abstract]
Consumer	46,578	32,576
Energy	10,278	12,842
Financial	45,470	31,186
Industrial	25,402	21,145
Technology	13,061	8,858
Funds (e.g. mutual funds, closed end funds, ETFs)	50,291	6,995
Other	10,683	6,343
Total equity securities	201,763	119,945
Short term	1,000	1,500
Cash equivalents	59,173	59,683
Total fair value	783,789	673,032
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	3,135	3,117
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	3,135	3,117
Equity securities [Abstract]
Consumer	46,578	32,576
Energy	10,278	12,842
Financial	45,470	30,943
Industrial	25,402	20,262
Technology	13,061	8,858
Funds (e.g. mutual funds, closed end funds, ETFs)	45,276	0
Other	10,683	6,343
Total equity securities	196,748	111,824
Short term	1,000	1,500
Cash equivalents	0	0
Total fair value	200,883	116,441
Recurring [Member] | Level 2 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	16,586	6,171
Agency mortgage-backed securities	27,075	4,770
Asset-backed securities	43,469	37,919
Bank loans	19,488	0
Certificates of deposit	0	0
Collateralized mortgage obligations	6,492	6,409
Corporate securities	193,058	135,794
Options embedded in convertible securities	5,291	4,751
Mortgage-backed securities	24,204	22,206
Municipal obligations	96,650	129,190
Non-U.S. government obligations	37,394	24,419
U.S. government obligations	49,011	91,940
Total fixed maturities	518,718	463,569
Equity securities [Abstract]
Consumer	0	0
Energy	0	0
Financial	0	243
Industrial	0	883
Technology	0	0
Funds (e.g. mutual funds, closed end funds, ETFs)	5,015	6,995
Other	0	0
Total equity securities	5,015	8,121
Short term	0	0
Cash equivalents	59,173	59,683
Total fair value	582,906	531,373
Recurring [Member] | Level 3 [Member]
Fixed maturities [Abstract]
Agency collateralized mortgage obligations	0	0
Agency mortgage-backed securities	0	0
Asset-backed securities	0	7,264
Bank loans	0	10,349
Certificates of deposit	0	0
Collateralized mortgage obligations	0	2,695
Corporate securities	0	2,138
Options embedded in convertible securities	0	0
Mortgage-backed securities	0	2,365
Municipal obligations	0	145
Non-U.S. government obligations	0	262
U.S. government obligations	0	0
Total fixed maturities	0	25,218
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	$ 25,218