Investment Securities - Narrative (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investment Securities
Accumulated other comprehensive income (loss) before tax amount	$ 31,400,000				$ 31,400,000		$ (7,900,000)
Accumulated other comprehensive income (loss), net of tax	22,358,000				22,358,000		(5,601,000)
Average balance of repurchase agreement facilities							15,000,000.0
Gross gains	406,000		$ 330,000	$ 1,000,000.0	1,400,000	$ 336,000
Gross losses	194,000		0	615,000	809,000	0
Proceeds from available-for-sale securities	57,200,000		16,200,000	$ 168,800,000	227,100,000	$ 16,200,000
FHLB stock	17,300,000				17,300,000
FRB stock	51,600,000				51,600,000
Other stock	23,900,000				$ 23,900,000
Amount of stock repurchased by FHLB	$ 5,400,000	$ 12,900,000	$ 0
HOA
Investment Securities
Value of inverse putable reverse repurchases secured by collateral							75,000
Mortgage-backed securities: residential
Investment Securities
Estimated par value of securities pledged as collateral for the Bank's inverse putable reverse repurchases							20,300,000
Fair value of securities pledged as collateral for the Bank's inverse putable reverse repurchases							$ 20,900,000