Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Values (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale	$ 0
Amortized Cost		$ 937,828,000	$ 939,160,000
Gross Unrealized Gains		26,470,000	14,660,000
Gross Unrealized Losses		(3,206,000)	(1,508,000)
Fair Value		961,092,000	952,312,000
U.S. Treasury and U.S. Government-sponsored agencies
Investment Holdings [Line Items]
Amortized Cost		85,868,000	104,709,000
Gross Unrealized Gains		1,314,000	598,000
Gross Unrealized Losses		(120,000)	(84,000)
Fair Value		87,062,000	105,223,000
Municipal securities
Investment Holdings [Line Items]
Amortized Cost		174,614,000	128,183,000
Gross Unrealized Gains		5,409,000	4,933,000
Gross Unrealized Losses		(415,000)	(102,000)
Fair Value		179,608,000	133,014,000
Residential
Investment Holdings [Line Items]
Amortized Cost		313,710,000	336,929,000
Gross Unrealized Gains		9,204,000	3,184,000
Gross Unrealized Losses		(230,000)	(505,000)
Fair Value		322,684,000	339,608,000
Commercial
Investment Holdings [Line Items]
Amortized Cost		316,683,000	322,169,000
Gross Unrealized Gains		10,348,000	5,575,000
Gross Unrealized Losses		(1,275,000)	(649,000)
Fair Value		325,756,000	327,095,000
Corporate obligations
Investment Holdings [Line Items]
Amortized Cost		23,897,000	23,893,000
Gross Unrealized Gains		195,000	316,000
Gross Unrealized Losses		(260,000)	(15,000)
Fair Value		23,832,000	24,194,000
Other asset-backed securities
Investment Holdings [Line Items]
Amortized Cost		23,056,000	23,277,000
Gross Unrealized Gains		0	54,000
Gross Unrealized Losses		(906,000)	(153,000)
Fair Value		$ 22,150,000	$ 23,178,000