Loans and Leases Held for Investment and Credit Quality - Summary of Risk Grades of Each Category of Loans (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,639,840	$ 1,850,480
Risk Grades 1 - 4
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,369,552	1,702,491
Risk Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	149,954	65,484
Risk Grades 6 - 8
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	120,334	82,505
Loans Insured or Guaranteed by US Government Authorities
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	700,600	305,400
Loans Insured or Guaranteed by US Government Authorities | Risk Grades 1 - 4
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	561,600	236,100
Loans Insured or Guaranteed by US Government Authorities | Risk Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	57,500	10,100
Loans Insured or Guaranteed by US Government Authorities | Risk Grades 6 - 8
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 81,600	$ 59,200