Investment Securities - Summary of Unrealized Loss Positions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) security
Investments in an unrealized loss position
Amount of pretax loss if securities in an unrealized loss position are sold	$ 8,000		$ 8,000
Sales of debt securities, available-for-sale	2,100		2,794
Sales of investment securities, available-for-sale		$ 19,000		$ 52,108
Gain on sale of debt securities	27		352	827
Gain on sale of available-for-sale securities		111		827
Loss on sale of debt securities	26		25	372
Loss on sale of available-for-sale securities		$ 6		$ 372
Sales of investment securities available-for-sale, unrealized gain	623		583
Investments in an Unrealized Loss Position
Less than 12 months, fair value	83,320		83,320		$ 88,519
Less than 12 months, unrealized loss	(2,347)		(2,347)		(884)
12 months or more, fair value	102,453		102,453		61,917
12 months or more, unrealized loss	$ (5,682)		$ (5,682)		$ (1,612)
U. S. Agency securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	56		56		45
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 35,654		$ 35,654		$ 61,834
Less than 12 months, unrealized loss	(837)		(837)		(659)
12 months or more, fair value	42,058		42,058		7,709
12 months or more, unrealized loss	$ (1,937)		$ (1,937)		$ (182)
U.S. Sponsored Mortgage-backed securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	42		42		39
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 11,646		$ 11,646		$ 16,825
Less than 12 months, unrealized loss	(493)		(493)		(159)
12 months or more, fair value	39,309		39,309		37,427
12 months or more, unrealized loss	$ (2,435)		$ (2,435)		$ (1,105)
Municipal securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	97		97		47
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 34,043		$ 34,043		$ 8,826
Less than 12 months, unrealized loss	(973)		(973)		(48)
12 months or more, fair value	20,585		20,585		16,781
12 months or more, unrealized loss	$ (1,290)		$ (1,290)		$ (325)
Other securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	4		4
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 1,977		$ 1,977
Less than 12 months, unrealized loss	(44)		(44)
12 months or more, fair value	501		501
12 months or more, unrealized loss	$ (20)		$ (20)
Equity and other securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security					2
Investments in an Unrealized Loss Position
Less than 12 months, fair value					$ 1,034
Less than 12 months, unrealized loss					(18)
12 months or more, fair value					0
12 months or more, unrealized loss					$ 0