Segment Information - Reconciliation of Operating Segments by Individual Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	$ 7,331	$ 15,052
Other operating expenses of the Corporate and Other segment	(8,279)	(7,906)
Underwriting (loss) profit	(948)	7,146
Net investment income	20,836	19,431
Net realized and unrealized (losses) gains on investments	(58,407)	1,625
Amortization of intangible assets	(149)	(149)
Other income and expenses	326	246
Interest expense	(2,876)	(2,808)
(Loss) income before taxes	(41,218)	25,491
Excess and Surplus Lines
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	8,112	13,102
Net investment income	7,941	5,544
Interest expense	0	0
Specialty Admitted Insurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	(988)	1,623
Net investment income	928	897
Interest expense	0	0
Casualty Reinsurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	207	327
Net investment income	11,604	11,172
Interest expense	$ 0	$ 0