Investment Securities - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investment Securities
Accumulated other comprehensive income (loss) before tax amount	$ 42,500,000			$ 42,500,000		$ (7,900,000)
Accumulated other comprehensive income (loss), net of tax	30,195,000			30,195,000		(5,601,000)
Average balance of repurchase agreement facilities						15,000,000.0
Other than temporary impairment losses				0	$ 0
Gross gains	5,100,000	$ 406,000	$ 1,300,000	6,500,000	1,600,000
Gross losses	811,000	194,000	208,000	1,600,000	208,000
Proceeds from available-for-sale securities	191,300,000	57,200,000	378,500,000	418,500,000	$ 394,500,000
FHLB stock	17,300,000			17,300,000
FRB stock	51,600,000			51,600,000
Other stock	$ 24,000,000.0			24,000,000.0
Amount of stock repurchased by FHLB		$ 5,400,000	$ 15,000,000.0
Impairment loss on investments in FHLB, FRB and other stock				$ 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