Investments - Debt and Short-term Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Investment Holdings [Line Items]
Other investments	$ 59,730		$ 59,730		$ 47,922
Investment in federal home loan bank stock	us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember
Cash and Short-term Investments
Investment in unconsolidated investees	$ 56,110		$ 56,110		$ 58,275
Cash	18,445		18,445		22,818
Short-term investments	125,032		125,032		36,229
Prime Holdings Insurance Services, Inc. (Prime)
Cash and Short-term Investments
Investment in unconsolidated investees	56,000		56,000
Other Unconsolidated Investees | Maximum
Cash and Short-term Investments
Investment in unconsolidated investees	1,000		1,000
FHLBC
Investment Holdings [Line Items]
Investments pledged as collateral	57,000		57,000
Federal home loan bank borrowings fair value disclosure	50,000		50,000
Investment In Low Income Housing Tax Credit Partnerships (LIHTC)
Investment Holdings [Line Items]
Other investments	11,000		11,000		13,000
Amortization on low income housing investments	800	$ 800	2,300	$ 2,500
Total tax benefit on investments in housing tax credit partnership	800	900	2,400	2,600
Qualified affordable housing project investments, unfunded commitment	1,000		1,000
Historic tax credit partnerships (HTC)
Investment Holdings [Line Items]
Other investments	14,000		14,000
Amortization on qualifying equity investments	1,100		3,400
Total tax benefit on investments in housing tax credit partnership	1,400	$ 1,300	4,300	$ 3,900
Equity investments in tax credit structures, unfunded commitment	1,000		1,000
Cash and Short-term Investments
Investment in unconsolidated investees					11,000
Investment in Private Funds
Investment Holdings [Line Items]
Other investments	27,000		27,000		$ 28,000
Fair value investments entities that calculate net asset value per share, unfunded commitments	$ 5,000		$ 5,000