Commitments, Guarantees and Contingent Liabilities - Maximum obligation to extend credit (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments to make loans	$ 406,881	$ 178,811
Unused lines of credit	927,806	433,109
Standby letters of credit	19,429	14,215
Total	$ 1,354,116	$ 626,135