Debt Securities Held to Maturity - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) security
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity, amortized cost, maturity, allocated and single maturity date, after year one through five	$ 5,000,000.0		$ 5,000,000.0
Debt securities, held-to-maturity, fair value, maturity, allocated and single maturity date, after year one through five	5,000,000.0		5,000,000.0
Debt securities, held-to-maturity	272,712,000		272,712,000		$ 285,756,000
Fair value	288,439,000		288,439,000		289,505,000
Proceeds from sale of held-to-maturity securities	0	$ 0	0	$ 0
Proceeds from sale and maturity of held-to-maturity securities	20,000,000.0	23,400,000	20,000,000.0	28,400,000
Debt securities, held-to-maturity, sold, realized gain (loss)	0		0
Debt securities, held-to-maturity, sold, realized		24,000		24,000
Debt securities, held-to-maturity, sold, realized loss		0		0
Fair value of securities sold under agreements to repurchase	$ 235,300,000		$ 235,300,000		$ 236,000,000.0
Number of positions | security	3		3		22
Other-than-temporary impairment loss, held-to-maturity, before tax	$ 0	$ 0	$ 0	$ 0
Mortgage-backed securities and collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	267,712,000		267,712,000		$ 265,756,000
Fair value	$ 283,435,000		$ 283,435,000		$ 269,545,000