Investments - Summary of Private Debt and Equity Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income [Line Items]
Total other invested assets	$ 61,210	$ 72,321
Investment Income	6,254	5,165	$ 14,079
Distributions from equity method investments	2,834	7,499	7,333
Equity in net income of subsidiaries	4,598	3,540	13,209
Renewable energy LLCs
Net Investment Income [Line Items]
Total other invested assets	31,219	29,795
Investment Income	2,181	2,974	10,578
Renewable energy notes receivable
Net Investment Income [Line Items]
Total other invested assets	8,750	8,750
Investment Income	$ 1,313	1,282	526
Investment interest rate	15.00%
Interest income	$ 1,300	1,300	526
Limited partnerships
Net Investment Income [Line Items]
Total other invested assets	16,741	29,276
Investment Income	2,417	566	2,632
Bank holding companies
Net Investment Income [Line Items]
Total other invested assets	4,500	4,500
Investment Income	343	343	343
Corporate and other segment | Limited partnerships
Net Investment Income [Line Items]
Carrying value of investments	3,400	3,100
Equity in net income of subsidiaries	327	70	394
Excess and Surplus Lines | Limited partnerships
Net Investment Income [Line Items]
Carrying value of investments	13,300	26,200
Equity in net income of subsidiaries	2,100	496	2,200
Commitment to investment in limited partnership	625
Investment in LLC | Corporate and other segment
Net Investment Income [Line Items]
Distributions from equity method investments	$ 757	5,800
Bank Holding Company
Net Investment Income [Line Items]
Investment interest rate	7.60%
Interest income	$ 343	$ 343	$ 343
Investment in subordinated notes	$ 4,500
Minimum | Investment in LLC | Corporate and other segment
Net Investment Income [Line Items]
Ownership percentage	2.60%
Maximum | Investment in LLC | Corporate and other segment
Net Investment Income [Line Items]
Ownership percentage	32.20%