Debt Securities - AFS Debt Securities in an Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Available-for-sale, Fair Value
Number of securities | security	65	88
Less than 12 months, fair value	$ 324,015	$ 289,499
Less than 12 months, unrealized loss	(1,002)	(1,608)
12 months or more, fair value	690	46,637
12 months or more, unrealized loss	(9)	(479)
Total, fair value	324,705	336,136
Total, unrealized loss	$ (1,011)	$ (2,087)
U.S. government and federal agency
Available-for-sale, Fair Value
Number of securities | security	19	20
Less than 12 months, fair value	$ 13,656	$ 464
Less than 12 months, unrealized loss	(230)	0
12 months or more, fair value	663	9,902
12 months or more, unrealized loss	(9)	(65)
Total, fair value	14,319	10,366
Total, unrealized loss	$ (239)	$ (65)
State and local governments
Available-for-sale, Fair Value
Number of securities | security	11	12
Less than 12 months, fair value	$ 5,383	$ 19,044
Less than 12 months, unrealized loss	(38)	(80)
12 months or more, fair value	0	0
12 months or more, unrealized loss	0	0
Total, fair value	5,383	19,044
Total, unrealized loss	$ (38)	$ (80)
Corporate bonds
Available-for-sale, Fair Value
Number of securities | security	6	2
Less than 12 months, fair value	$ 11,029	$ 7,378
Less than 12 months, unrealized loss	(23)	(1)
12 months or more, fair value	0	0
12 months or more, unrealized loss	0	0
Total, fair value	11,029	7,378
Total, unrealized loss	$ (23)	$ (1)
Residential mortgage-backed securities
Available-for-sale, Fair Value
Number of securities | security	28	35
Less than 12 months, fair value	$ 282,912	$ 85,562
Less than 12 months, unrealized loss	(709)	(234)
12 months or more, fair value	27	29,038
12 months or more, unrealized loss	0	(315)
Total, fair value	282,939	114,600
Total, unrealized loss	$ (709)	$ (549)
Commercial mortgage-backed securities
Available-for-sale, Fair Value
Number of securities | security	1	19
Less than 12 months, fair value	$ 11,035	$ 177,051
Less than 12 months, unrealized loss	(2)	(1,293)
12 months or more, fair value	0	7,697
12 months or more, unrealized loss	0	(99)
Total, fair value	11,035	184,748
Total, unrealized loss	$ (2)	$ (1,392)