Securities - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2013	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 0			$ 0
Available-for-sale securities transferred to held-to-maturity securities			$ 536,000,000.0
Unrealized net loss on securities transferred from available-for-sale to held-to-maturity, gross			$ 13,300,000
Realized gains on the sale of available-for-sale securities	244,000			244,000
Realized gain or losses on the sale of available-for-sale securities		$ 0			$ 0
Equity securities, realized loss	0	$ 0		53,000	$ 0
Corporate debt securities, callable, amortized cost	38,500,000			38,500,000
Corporate debt securities, callable, estimated fair value	39,800,000			39,800,000
Securities pledged for other debt obligations, at fair value	456,600,000			456,600,000		$ 475,600,000
Reverse Repurchase Agreement
Debt Securities, Available-for-sale [Line Items]
Securities pledged for repurchase agreements, at fair value	$ 148,100,000			$ 148,100,000		$ 81,400,000