Fair Value - Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Assets
Derivative financial instruments	$ 172,800,000	$ 209,800
Trading securities	56,580	31,263
Securities available for sale	4,949,334	5,326,822
SBA servicing asset	6,200	6,100
Liabilities
Derivative financial instruments	974,500,000	1,000,000
U.S. Treasuries
Assets
Securities available for sale	219,913	265,638
U.S. Government agencies
Assets
Trading securities	11,049	11,190
Securities available for sale	218,345	219,088
Residential mortgage pass-through securities issued or guaranteed by U.S. government agencies or sponsored enterprises
Assets
Trading securities	8,265
Securities available for sale	1,604,370	1,698,353
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Trading securities	11,705	4,589
Securities available for sale	962,494	1,000,398
State and municipal obligations
Assets
Trading securities	20,298	13,993
Securities available for sale	954,455	1,064,852
Small Business Administration loan-backed securities
Assets
Securities available for sale	404,559	444,810
Corporate securities.
Assets
Securities available for sale	25,422	32,638
Significant Other Observable Inputs (Level 2)
Assets
Loans held for sale	42,951	28,968
Trading securities	56,580	31,263
Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	87,539	86,610
SBA servicing asset	6,202	6,068
Changes in fair value of assets
Changes in hierarchy classifications of Level 3 assets	0
Changes in hierarchy classifications of Level 3 liabilities	0
Recurring basis
Assets
Derivative financial instruments	174,480	211,016
Loans held for sale	42,951	28,968
Trading securities	56,580	31,263
Securities available for sale	4,949,334	5,326,822
Mortgage servicing rights	87,539	86,610
SBA servicing asset	6,202	6,068
Fair value of Assets, Total	5,317,086	5,690,747
Liabilities
Derivative financial instruments	975,717	1,034,143
Recurring basis | U.S. Treasuries
Assets
Securities available for sale	219,913	265,638
Recurring basis | U.S. Government agencies
Assets
Securities available for sale	218,345	219,088
Recurring basis | Residential mortgage pass-through securities issued or guaranteed by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	1,604,370	1,698,353
Recurring basis | Residential Collateralized Mortgage-Obligations Issued By U.S. Government Agencies Or Sponsored Enterprises [Member]
Assets
Securities available for sale	559,776	601,045
Recurring basis | Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	962,494	1,000,398
Recurring basis | State and municipal obligations
Assets
Securities available for sale	954,455	1,064,852
Recurring basis | Small Business Administration loan-backed securities
Assets
Securities available for sale	404,559	444,810
Recurring basis | Corporate securities.
Assets
Securities available for sale	25,422	32,638
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	174,480	211,016
Loans held for sale	42,951	28,968
Trading securities	56,580	31,263
Securities available for sale	4,949,334	5,326,822
Fair value of Assets, Total	5,223,345	5,598,069
Liabilities
Derivative financial instruments	975,717	1,034,143
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Treasuries
Assets
Securities available for sale	219,913	265,638
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government agencies
Assets
Securities available for sale	218,345	219,088
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential mortgage pass-through securities issued or guaranteed by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	1,604,370	1,698,353
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential Collateralized Mortgage-Obligations Issued By U.S. Government Agencies Or Sponsored Enterprises [Member]
Assets
Securities available for sale	559,776	601,045
Recurring basis | Significant Other Observable Inputs (Level 2) | Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	962,494	1,000,398
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets
Securities available for sale	954,455	1,064,852
Recurring basis | Significant Other Observable Inputs (Level 2) | Small Business Administration loan-backed securities
Assets
Securities available for sale	404,559	444,810
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate securities.
Assets
Securities available for sale	25,422	32,638
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	87,539	86,610
SBA servicing asset	6,202	6,068
Fair value of Assets, Total	93,741	$ 92,678
Changes in fair value of assets
Unrealized losses included in accumulated other comprehensive (loss) income related to Level 3 financial assets and liabilities	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Mortgage Servicing Rights
Changes in fair value of assets
Fair value of assets at the beginning of the period	86,610
Servicing assets that resulted from transfers of financial assets	4,034
Changes in fair value assets due to valuation inputs or assumptions	$ 688
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax
Changes in fair value due to decay	$ (3,793)
Fair value of assets at the end of the period	87,539
Recurring basis | Significant Unobservable Inputs (Level 3) | SBA servicing asset
Changes in fair value of assets
Fair value of assets at the beginning of the period	6,068
Servicing assets that resulted from transfers of financial assets	631
Changes in fair value assets due to valuation inputs or assumptions	$ 434
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax
Changes in fair value due to decay	$ (931)
Fair value of assets at the end of the period	$ 6,202