Segment Information - Reconciliation of Operating Segments by Individual Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	$ 14,888	$ 17,008	$ 22,219	$ 32,060
Other operating expenses of the Corporate and Other segment	(7,472)	(7,433)	(15,751)	(15,339)
Underwriting profit	7,416	9,575	6,468	16,721
Net investment income	15,350	17,535	36,186	36,966
Net realized and unrealized gains (losses) on investments	21,593	1,063	(36,814)	2,688
Amortization of intangible assets	(149)	(149)	(298)	(298)
Other income and expenses	(1,485)	(378)	(1,159)	(132)
Interest expense	(2,965)	(2,684)	(5,841)	(5,492)
Income (loss) before taxes	39,760	24,962	(1,458)	50,453
Excess and Surplus Lines
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	16,095	15,810	24,207	28,912
Net investment income	3,336	4,229	11,277	9,773
Interest expense	0	0	0	0
Specialty Admitted Insurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	1,430	1,298	442	2,921
Net investment income	812	918	1,740	1,815
Interest expense	0	0	0	0
Casualty Reinsurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	(2,637)	(100)	(2,430)	227
Net investment income	10,534	11,986	22,138	23,158
Interest expense	$ 0	$ 0	$ 0	$ 0