Summary of Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Jan. 18, 2017	Dec. 31, 2020 USD ($) employee subsidiary item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 04, 2017 shares
Summary Of Significant Accounting Policies [Line Items]
Number of inactive wholly owned subsidiaries | subsidiary		2
Number of full-time equivalent employees | employee		502
Cash and cash equivalents held at the Federal Reserve Bank		$ 623,000,000
Impaired long-lived assets		0	$ 0
Investment in FHLB stock		17,250,000	21,519,000
Allowances for servicing rights		1,400,000	0
Stock split, conversion ratio	2
Additional share of common stock following stock split | shares					1
Provision for credit losses		6,746,000	2,637,000	$ 4,220,000
Core Deposit
Summary Of Significant Accounting Policies [Line Items]
Core deposit intangible assets		6,800,000	8,700,000
Core deposit intangible amortization expense		1,900,000	$ 2,300,000	$ 2,000,000.0
FHLB Stock
Summary Of Significant Accounting Policies [Line Items]
Adjustments in carrying value		$ 0
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		3 years
Estimated useful lives of other intangible assets		7 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		10 years
Estimated useful lives of other intangible assets		10 years
California
Summary Of Significant Accounting Policies [Line Items]
Percentage of bank loans		91.00%
FFB
Summary Of Significant Accounting Policies [Line Items]
Approximate number of clients | item		1,500
Aggregate assets under management		$ 4,900,000,000