Loans and Leases Held for Investment and Credit Quality - Summary of Asset Quality Indicators by Portfolio Class and Origination Year (Parenthetical) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 4,715,992	$ 4,349,274
Loans receivable, fair value	743,226	815,374
Loans Insured or Guaranteed by US Government Authorities
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,510,000	2,610,000
Loans Insured or Guaranteed by US Government Authorities | Risk Grades 1 - 4
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,330,000	2,440,000
Loans Insured or Guaranteed by US Government Authorities | Risk Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	144,000	128,000
Loans Insured or Guaranteed by US Government Authorities | Risk Grades 6 - 8
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 42,200	$ 40,900