Investment Securities - Available-for-Sale Securities Amortized Cost and Fair Value (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	$ 952,278,000	$ 373,038,000
Available-for-sale, gross unrealized gains	14,351,000	19,393,000
Available-for-sale, gross unrealized losses	(3,596,000)	(80,000)
Allowance for Credit Losses	0	0
Available-for-sale securities	963,033,000	392,351,000
Accrued interest	2,900,000	1,900,000
MBS pass-through securities issued by FHLMC and FNMA
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	207,557,000	50,686,000
Available-for-sale, gross unrealized gains	1,925,000	2,530,000
Available-for-sale, gross unrealized losses	(243,000)	0
Allowance for Credit Losses	0	0
Available-for-sale securities	209,239,000	53,216,000
CMOs issued by FHLMC
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	363,708,000	143,267,000
Available-for-sale, gross unrealized gains	5,045,000	7,925,000
Available-for-sale, gross unrealized losses	(1,065,000)	(1,000)
Allowance for Credit Losses	0	0
Available-for-sale securities	367,688,000	151,191,000
CMOs issued by FNMA
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	55,178,000	16,450,000
Available-for-sale, gross unrealized gains	244,000	580,000
Available-for-sale, gross unrealized losses	(211,000)	0
Allowance for Credit Losses	0	0
Available-for-sale securities	55,211,000	17,030,000
CMOs issued by GNMA
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	61,411,000	6,863,000
Available-for-sale, gross unrealized gains	232,000	351,000
Available-for-sale, gross unrealized losses	(249,000)	0
Allowance for Credit Losses	0	0
Available-for-sale securities	61,394,000	7,214,000
SBA-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	33,422,000	30,941,000
Available-for-sale, gross unrealized gains	1,323,000	1,976,000
Available-for-sale, gross unrealized losses	(136,000)	(55,000)
Allowance for Credit Losses	0	0
Available-for-sale securities	34,609,000	32,862,000
Debentures of government- sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	71,328,000	19,944,000
Available-for-sale, gross unrealized gains	63,000	266,000
Available-for-sale, gross unrealized losses	(1,177,000)	(24,000)
Allowance for Credit Losses	0	0
Available-for-sale securities	70,214,000	20,186,000
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	11,881,000
Available-for-sale, gross unrealized gains	0
Available-for-sale, gross unrealized losses	(104,000)
Allowance for Credit Losses	0
Available-for-sale securities	11,777,000
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	131,865,000	104,887,000
Available-for-sale, gross unrealized gains	5,519,000	5,765,000
Available-for-sale, gross unrealized losses	(169,000)	0
Allowance for Credit Losses	0	0
Available-for-sale securities	137,215,000	$ 110,652,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	14,014,000
Available-for-sale, gross unrealized gains	0
Available-for-sale, gross unrealized losses	(237,000)
Allowance for Credit Losses	0
Available-for-sale securities	13,777,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, amortized cost	1,914,000
Available-for-sale, gross unrealized gains	0
Available-for-sale, gross unrealized losses	(5,000)
Allowance for Credit Losses	0
Available-for-sale securities	$ 1,909,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Section 50
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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