Securities - Contractual Maturities (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Contractual Maturities, Amortized Cost
Within one year		$ 198,771,000		$ 68,482,000
After one through five years		206,535,000		232,067,000
Contractual Maturities, Amortized Cost, Single Maturity Date		405,306,000		300,549,000
Available-for-sale Securities, Amortized Cost Basis, Total		431,373,000		326,931,000
Contractual Maturities, Fair Value
Within one year		198,340,000		68,426,000
After one through five years		206,174,000		231,066,000
Contractual Maturities, Fair Value, Single Maturity Date		404,514,000		299,492,000
Fair Value		430,581,000		325,874,000
Proceeds from the sale of securities available for sale		0	$ 7,371,000
Realized gross gains on available for sale securities	$ 24,000		$ 24,000
Mortgage-backed - Government-sponsored entity (GSE) - residential
Contractual Maturities, Amortized Cost
Mortgage-backed - Government-sponsored entity (GSE) - residential, Amortized Cost		26,067,000		26,382,000
Available-for-sale Securities, Amortized Cost Basis, Total		26,067,000		26,382,000
Contractual Maturities, Fair Value
Mortgage-backed - Government-sponsored entity (GSE) - residential, Fair Value		26,067,000		26,382,000
Fair Value		$ 26,067,000		$ 26,382,000