Investment Securities - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) security position	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) security position	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) security position
Investment Securities [Line Items]
Equity securities	$ 29,026,000		$ 29,026,000		$ 41,410,000
Number of security positions in the debt securities available for sale portfolio in an unrealized loss position (in security) | position	64		64		182
Fair value of debt securities available for sale pledged as collateral	$ 868,900,000		$ 868,900,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years			3 years 10 months 24 days
Amortized cost	1,479,966,000		$ 1,479,966,000		$ 1,558,787,000
Fair Value	1,526,564,000		1,526,564,000		$ 1,566,801,000
Impairment loss	0		0	$ 2,900,000
Allowance for credit losses	$ 0		$ 0
Number of security positions in the securities held to maturity portfolio in an unrealized loss position (in security) | security	20		20		82
Fair value of investments held to maturity pledged as collateral	$ 1,000,000,000.0		$ 1,000,000,000.0
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years			2 years 6 months
Forecast period			2 years
Historical loss experience period			1 year
Allowance for credit losses	1,481,000		$ 1,481,000
Provision for credit losses	(112,000)	$ 0	688,000	$ 0
Charge-offs of debt securities	0		0
US States and Political Subdivisions Debt Securities, Special Revenue Bonds
Investment Securities [Line Items]
Amortized cost	70,600,000		70,600,000
Fair Value	71,900,000		$ 71,900,000
Investment percentage			41.00%
US States And Political Subdivisions Debt Securities, Special Revenue Bonds, Impaired Securities
Investment Securities [Line Items]
Amortized cost	680,000		$ 680,000
Fair Value	$ 783,000		$ 783,000