Commitments and Contingencies - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies
Commitments to extend credit, fixed rate	$ 158,817,000	$ 133,641,000
Commitments to extend credit, variable rate	961,821,000	606,738,000
Commitment to extend credit, total	$ 1,120,638,000	740,379,000
Expiration term of commitments (in years)	1 year
Reserves in the form of vault cash and balances at Federal Reserve Bank of San Francisco	$ 48,717,000
Unused lines of credit and commitments to make loans
Commitments and Contingencies
Commitments to extend credit, fixed rate	147,372,000	130,871,000
Commitments to extend credit, variable rate	951,206,000	593,839,000
Commitment to extend credit, total	1,098,578,000	724,710,000
Standby letters of credit
Commitments and Contingencies
Commitments to extend credit, fixed rate	11,445,000	2,770,000
Commitments to extend credit, variable rate	10,615,000	12,899,000
Commitment to extend credit, total	$ 22,060,000	$ 15,669,000