Short-term borrowings (Details) - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Short-term borrowings [Abstract]
Remaining borrowing capacity	$ 2,100,000,000	$ 2,100,000,000
Loans held for investment	3,572,570,000	3,603,105,000
Unsecured borrowing capacity	133,000,000
FHLB of San Francisco [Member]
Short-term borrowings [Abstract]
Maximum borrowing capacity	890,400,000
Collateral amount	$ 1,100,000,000
Interest rate	3.89%
Federal Reserve Bank [Member]
Short-term borrowings [Abstract]
Remaining borrowing capacity	$ 1,100,000,000
Maximum borrowing capacity	1,100,000,000
Outstanding advances	$ 0	$ 0
Federal Reserve Bank [Member] | Asset Pledged as Collateral [Member]
Short-term borrowings [Abstract]
Interest rate	3.75%
Loans held for investment	$ 1,400,000,000