Investments - Debt and Short-term Investments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Investment Holdings [Line Items]
Other Investments	$ 59,988,000		$ 59,988,000		$ 70,441,000
Investment in Federal Home Loan Bank Stock	us-gaap:AssetPledgedAsCollateralMember		us-gaap:AssetPledgedAsCollateralMember
Cash and Short-term Investments
Cash	$ 70,589,000		$ 70,589,000		46,203,000
FHLBC
Investment Holdings [Line Items]
Investments pledged as collateral	13,700,000		13,700,000
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0		0
Investment In Low Income Housing Tax Credit Partnership Net Of Amortization
Investment Holdings [Line Items]
Other Investments	21,000,000.0		21,000,000.0		23,300,000
Total tax benefit on investments in housing tax credit partnership	900,000	$ 600,000	2,600,000	$ 1,900,000
Qualified Affordable Housing Project Investments, Commitment	4,700,000		4,700,000
Investment in Private Funds
Investment Holdings [Line Items]
Other Investments	26,500,000		26,500,000		$ 46,000,000.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	8,300,000		8,300,000
Investment in Restricted Stock
Investment Holdings [Line Items]
Other Investments	$ 10,600,000		$ 10,600,000