Reserve for Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020
Liability for Claims and Claims Adjustment Expense [Abstract]
Allowance for uncollectible reinsurance balances	$ 335		$ 335		$ 335
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	(4,234)	$ (56,971)	(6,234)	$ (60,254)
Excess and Surplus Lines
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	27	(50,000)	2,800	(51,200)
Specialty Admitted Insurance
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	2,000	1,000	4,000	4,300
Casualty Reinsurance
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	$ (6,200)	$ (7,900)	$ (13,100)	$ (13,300)