Loans Held for Investment - Narrative (Details)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Jun. 30, 2023 USD ($) loan borrowingRelationship	Jun. 30, 2022 loan	Jun. 30, 2023 USD ($) grade loan area borrowingRelationship	Jun. 30, 2022 loan	Dec. 31, 2022 USD ($) loan
Loans Held for Investment
Servicing rights retained from guaranteed portion of SBA loans sold		$ 2,300,000		$ 2,300,000		$ 3,000,000
Accrued expenses and other liabilities		227,351,000		227,351,000		206,023,000
Unpaid principal balance for loans and participations serviced for others		421,300,000		421,300,000		463,400,000
Secured loans limit to one borrower		824,200,000		824,200,000
Unsecured loans limit to one borrower		494,500,000		494,500,000
Aggregate outstanding balance of loans to one borrower of secured credit		170,300,000		$ 170,300,000
Number of areas where the entity's credit quality is maintained and credit risk managed | area				2
Number of pass scale grades | grade				6
Individually evaluated loans		17,200,000		$ 17,200,000		30,900,000
ACL attributable to individually evaluated loans		4,000,000		4,000,000		1,700,000
Loans held for investment		13,610,282,000		13,610,282,000		14,676,298,000
Total nonaccrual loans		$ 17,151,000		$ 17,151,000		30,905,000
Number of loans 90 days or more past due and still accruing | loan		7		7
Number of loans 90 days or more past due and still accruing, number of borrowing relationships | borrowingRelationship		1		1
Loans 90 days or more past due and still accruing						0
Consumer mortgage loans collateralized by residential real estate, foreclosure proceedings in process		$ 0		$ 0		$ 0
Loan modifications to borrowers		0		851,000
Preceding payment default		0		0
Number of loans modified | loan						5
Troubled debt restructuring						$ 16,100,000
Financial Asset Acquired with Credit Deterioration
Loans Held for Investment
Loans held for investment		393,500,000		393,500,000		422,700,000
Discounted Cash Flow Approach
Loans Held for Investment
Individually evaluated loans		$ 0		$ 0		0
Multifamily Loan Securitization, Liability | Variable Interest Entity, Not Primary Beneficiary
Loans Held for Investment
Maximum loss, percentage of loans		10.00%		10.00%
Accrued expenses and other liabilities		$ 334,000		$ 334,000		334,000
Multifamily Loan Securitization
Loans Held for Investment
Unpaid principal balance for loans and participations serviced for others		51,300,000		51,300,000		54,200,000
Multifamily Loan Securitization | Variable Interest Entity, Not Primary Beneficiary
Loans Held for Investment
Accrued expenses and other liabilities		334,000		334,000		334,000
Multifamily Loan Securitization | Opus Bank
Loans Held for Investment
Proceeds from sale of loans receivable	$ 509,000,000
SBA
Loans Held for Investment
Unpaid principal balance for loans and participations serviced for others		286,300,000		286,300,000		315,300,000
CRE owner-occupied & Commercial and industrial
Loans Held for Investment
Troubled debt restructuring						$ 5,100,000
CRE owner-occupied
Loans Held for Investment
Number of loans modified | loan			3		3	3
Commercial and industrial
Loans Held for Investment
Loans 90 days or more past due and still accruing		$ 17,900,000		$ 17,900,000
Number of loans modified | loan			1		1	1
Franchise non-real estate secured
Loans Held for Investment
Number of loans modified | loan						1
Troubled debt restructuring						$ 11,000,000