Unpaid Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year adjustments		$ 4,695,000	$ 2,703,000	$ 11,481,000	$ 7,076,000
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year adjustments		$ 4,700,000	2,700,000	$ 11,500,000
Amortization of deferred gain on ADC			$ 481,000,000,000
Personal Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year adjustments					7,100,000
Amortization of deferred gain on ADC					$ 5,700,000
Maximum | Adverse Development Cover Reinsurance Agreement [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Amount reinsured	$ 17,500,000