Investment Securities - Summary of Remaining Contractual Principal Maturities for Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	$ 81,995,000	$ 17,217,000
U.S. agency debentures
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	622,000	421,000
Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	52,526,000	7,978,000
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations—fixed rate
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	7,358,000	1,758,000
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations—variable rate
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	110,000	138,000
Agency-issued commercial mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	14,289,000	3,067,000
Municipal bonds and notes
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	6,558,000	$ 3,855,000
After One Year to Five Years, Amortized Cost	157,000
After Five Years to Ten Years, Amortized Cost	973,000
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	532,000
After One Year to Five Years, Amortized Cost	0
After Five Years to Ten Years, Amortized Cost	533,000
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	82,371,000
Fair Value	81,995,000
One Year or Less, Amortized Cost	54,000
One Year or Less, Fair Value	55,000
After One Year to Five Years, Amortized Cost	517,000
After One Year to Five Years, Fair Value	526,000
After Five Years to Ten Years, Amortized Cost	3,283,000
After Five Years to Ten Years, Fair Value	3,368,000
After Ten Years, Amortized Cost	78,517,000
After Ten Years, Fair Value	$ 78,046,000
Held-to-maturity Securities | Lower Limit
Schedule of Held-to-maturity Securities [Line Items]
Mortgage-backed securities contractual maturities (in years)	10 years
Held-to-maturity Securities | Upper Limit
Schedule of Held-to-maturity Securities [Line Items]
Mortgage-backed securities contractual maturities (in years)	30 years
Held-to-maturity Securities | U.S. agency debentures
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 609,000
Fair Value	622,000
One Year or Less, Amortized Cost	1,000
One Year or Less, Fair Value	1,000
After One Year to Five Years, Amortized Cost	133,000
After One Year to Five Years, Fair Value	137,000
After Five Years to Ten Years, Amortized Cost	475,000
After Five Years to Ten Years, Fair Value	484,000
After Ten Years, Amortized Cost	0
After Ten Years, Fair Value	0
Held-to-maturity Securities | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	52,874,000
Fair Value	52,526,000
One Year or Less, Amortized Cost	1,000
One Year or Less, Fair Value	2,000
After One Year to Five Years, Amortized Cost	7,000
After One Year to Five Years, Fair Value	8,000
After Five Years to Ten Years, Amortized Cost	407,000
After Five Years to Ten Years, Fair Value	419,000
After Ten Years, Amortized Cost	52,459,000
After Ten Years, Fair Value	52,097,000
Held-to-maturity Securities | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations—fixed rate
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7,410,000
Fair Value	7,358,000
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year to Five Years, Amortized Cost	7,000
After One Year to Five Years, Fair Value	7,000
After Five Years to Ten Years, Amortized Cost	361,000
After Five Years to Ten Years, Fair Value	368,000
After Ten Years, Amortized Cost	7,042,000
After Ten Years, Fair Value	6,983,000
Held-to-maturity Securities | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations—variable rate
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	109,000
Fair Value	110,000
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year to Five Years, Amortized Cost	0
After One Year to Five Years, Fair Value	0
After Five Years to Ten Years, Amortized Cost	0
After Five Years to Ten Years, Fair Value	0
After Ten Years, Amortized Cost	109,000
After Ten Years, Fair Value	110,000
Held-to-maturity Securities | Agency-issued commercial mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,351,000
Fair Value	14,289,000
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year to Five Years, Amortized Cost	213,000
After One Year to Five Years, Fair Value	212,000
After Five Years to Ten Years, Amortized Cost	534,000
After Five Years to Ten Years, Fair Value	550,000
After Ten Years, Amortized Cost	13,604,000
After Ten Years, Fair Value	13,527,000
Held-to-maturity Securities | Municipal bonds and notes
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,485,000
Fair Value	6,558,000
One Year or Less, Amortized Cost	52,000
One Year or Less, Fair Value	52,000
After One Year to Five Years, Fair Value	162,000
After Five Years to Ten Years, Fair Value	1,015,000
After Ten Years, Amortized Cost	5,303,000
After Ten Years, Fair Value	5,329,000
Held-to-maturity Securities | Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	533,000
Fair Value	532,000
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year to Five Years, Fair Value	0
After Five Years to Ten Years, Fair Value	532,000
After Ten Years, Amortized Cost	0
After Ten Years, Fair Value	$ 0