Investment Securities - Summary of Unrealized Loss Positions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) security	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) security	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 14,592,000		$ 14,592,000		$ 20,510,000
Less than 12 months, unrealized loss	(38,000)		(38,000)		(249,000)
12 months or more, fair value	57,033,000		57,033,000		148,468,000
12 months or more, unrealized loss	(751,000)		(751,000)		(4,675,000)
Carrying value of investment securities pledged	60,200,000		60,200,000
Amount of pretax loss if securities in an unrealized loss position are sold	789,000		789,000
Sales of debt securities, available-for-sale	380,000	$ 2,100,000	26,996,000	$ 2,794,000
Gain on sale of debt securities	0	27,000	80,000	352,000
Loss on sale of debt securities	11,000	26,000	259,000	25,000
Sales of equity securities	0	0	6,000,000.0	0
Gain on sale of equity securities			0	0
Loss on sale of equity securities			(7,000)	0
Sales of investment securities available-for-sale, unrealized gain (loss)	0	$ (623,000)	13,800,000	$ (583,000)
U. S. Agency securities
Investments in an Unrealized Loss Position
Less than 12 months, fair value	8,244,000		8,244,000		9,762,000
Less than 12 months, unrealized loss	(18,000)		(18,000)		(123,000)
12 months or more, fair value	23,455,000		23,455,000		63,740,000
12 months or more, unrealized loss	$ (200,000)		$ (200,000)		$ (1,502,000)
Number of investments in an unrealized loss position | security	26		26		54
U.S. Sponsored Mortgage-backed securities
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 4,175,000		$ 4,175,000		$ 2,360,000
Less than 12 months, unrealized loss	(6,000)		(6,000)		(32,000)
12 months or more, fair value	32,237,000		32,237,000		47,755,000
12 months or more, unrealized loss	$ (532,000)		$ (532,000)		$ (2,007,000)
Number of investments in an unrealized loss position | security	33		33		42
Municipal securities
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 2,173,000		$ 2,173,000		$ 5,936,000
Less than 12 months, unrealized loss	(14,000)		(14,000)		(46,000)
12 months or more, fair value	831,000		831,000		35,955,000
12 months or more, unrealized loss	$ (16,000)		$ (16,000)		$ (1,146,000)
Number of investments in an unrealized loss position | security	6		6		78
Other securities
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 0		$ 0		$ 2,452,000
Less than 12 months, unrealized loss	0		0		(48,000)
12 months or more, fair value	510,000		510,000		1,018,000
12 months or more, unrealized loss	$ (3,000)		$ (3,000)		$ (20,000)
Number of investments in an unrealized loss position | security	1		1		2