Investment Securities - Summary of Unrealized Loss Positions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Investments in an unrealized loss position
Amount of pretax loss if securities in an unrealized loss position are sold	$ 1,800,000		$ 1,800,000
Investments in an Unrealized Loss Position
Less than 12 months, fair value	56,353,000		56,353,000		$ 104,750,000
Less than 12 months, unrealized loss	(567,000)		(567,000)		(3,488,000)
12 months or more, fair value	52,848,000		52,848,000		13,919,000
12 months or more, unrealized loss	(1,227,000)		(1,227,000)		$ (322,000)
Available-for-sale Securities
Available-for-sale investments sold	19,000,000	$ 15,700,000	52,108,000	$ 55,191,000
Gains on the sale of available-for-sale investments	111,000	479,000	827,000	1,100,000
Losses on the sale of available-for-sale investments	6,000	0	372,000	2,000
Held-to-maturity Securities
Sales of investment securities	$ 0	$ 0	$ 0	$ 0
U. S. Agency securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	23		23		16
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 29,921,000		$ 29,921,000		$ 28,814,000
Less than 12 months, unrealized loss	(206,000)		(206,000)		(425,000)
12 months or more, fair value	6,859,000		6,859,000		0
12 months or more, unrealized loss	$ (141,000)		$ (141,000)		$ 0
U.S. Sponsored Mortgage-backed securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	33		33		29
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 19,186,000		$ 19,186,000		$ 33,209,000
Less than 12 months, unrealized loss	(287,000)		(287,000)		(1,040,000)
12 months or more, fair value	27,400,000		27,400,000		13,919,000
12 months or more, unrealized loss	$ (657,000)		$ (657,000)		$ (322,000)
Municipal securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	48		48		86
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 7,246,000		$ 7,246,000		$ 42,727,000
Less than 12 months, unrealized loss	(74,000)		(74,000)		(2,023,000)
12 months or more, fair value	18,589,000		18,589,000		0
12 months or more, unrealized loss	$ (429,000)		$ (429,000)		$ 0
Equity and other securities
Investments in an unrealized loss position
Number of investments in an unrealized loss position | security	0		0
Investments in an Unrealized Loss Position
Less than 12 months, fair value	$ 0		$ 0
Less than 12 months, unrealized loss	0		0
12 months or more, fair value	0		0
12 months or more, unrealized loss	$ 0		$ 0