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Investments - Summary of Private Debt and Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Net Investment Income [Line Items]
Total other invested assets	$ 47,697		$ 61,210
Investment income	517	$ 3,404
Interest income		5,100
Renewable energy LLCs
Net Investment Income [Line Items]
Total other invested assets	31,305		31,219
Investment income	834	921
Renewable energy notes receivable
Net Investment Income [Line Items]
Total other invested assets	2,680		8,750
Investment income	166	328
Repayment received	$ 6,100
Rate of interest	15.00%
Limited partnerships
Net Investment Income [Line Items]
Total other invested assets	$ 9,212		16,741
Investment income	(569)	2,069
Bank holding companies
Net Investment Income [Line Items]
Total other invested assets	4,500		$ 4,500
Investment income	86	86
Interest income	$ 86	86
Bank Holding Company
Net Investment Income [Line Items]
Rate of interest	7.60%
Corporate and Other \| Limited partnerships
Net Investment Income [Line Items]
Carrying values of limited partnerships held	$ 2,700
Investment income (loss)	710	481
Corporate and Other \| Investment in LLC
Net Investment Income [Line Items]
Cash distributions from LLCs	747	253
Corporate and Other \| Bank Holding Company
Net Investment Income [Line Items]
Investment in private subordinated notes	4,500
Excess and Surplus Lines \| Limited partnerships
Net Investment Income [Line Items]
Carrying values of limited partnerships held	6,500
Investment income (loss)	$ 141	$ 1,600
Minimum \| Corporate and Other \| Investment in LLC
Net Investment Income [Line Items]
Ownership percentage	2.60%
Maximum \| Corporate and Other \| Investment in LLC
Net Investment Income [Line Items]
Ownership percentage	32.20%