Fair Value - Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Assets
Trading securities	$ 74,234	$ 77,689
Securities available for sale	5,924,206	5,193,478
U.S. Treasuries
Assets
Securities available for sale	268,581
U.S. Government agencies
Assets
Trading securities	14,801	5,154
Securities available for sale	179,942	97,117
Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Trading securities	26,484	6,853
Securities available for sale	2,013,904	1,831,039
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Trading securities	10,973	29,667
Securities available for sale	1,151,860	1,207,241
State and municipal obligations
Assets
Trading securities	12,078	20,798
Securities available for sale	1,127,697	812,689
Corporate securities.
Assets
Securities available for sale	30,160	18,734
Significant Other Observable Inputs (Level 2)
Assets
Loans held for sale	130,376	191,723
Trading securities	74,234	77,689
Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	83,339	65,620
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	412,815	414,742
Loans held for sale	130,376	191,723
Trading securities	74,234	77,689
Securities available for sale	5,924,206	5,193,478
Mortgage servicing rights	83,339	65,620
Fair value of Assets, Total	6,624,970	5,943,252
Liabilities
Derivative financial instruments	412,168	410,137
Recurring basis | U.S. Treasuries
Assets
Securities available for sale	268,581
Recurring basis | U.S. Government agencies
Assets
Securities available for sale	179,942	97,117
Recurring basis | Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	2,013,904	1,831,039
Recurring basis | Residential Collateralized Mortgage-Obligations Issued By U.S. Government Agencies Or Sponsored Enterprises [Member]
Assets
Securities available for sale	694,705	725,995
Recurring basis | Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	1,151,860	1,207,241
Recurring basis | State and municipal obligations
Assets
Securities available for sale	1,127,697	812,689
Recurring basis | Mortgage-backed securities
Assets
Securities available for sale	457,357	500,663
Recurring basis | Corporate securities.
Assets
Securities available for sale	30,160	18,734
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	412,815	414,742
Loans held for sale	130,376	191,723
Trading securities	74,234	77,689
Securities available for sale	5,924,206	5,193,478
Fair value of Assets, Total	6,541,631	5,877,632
Liabilities
Derivative financial instruments	412,168	410,137
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Treasuries
Assets
Securities available for sale	268,581
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government agencies
Assets
Securities available for sale	179,942	97,117
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	2,013,904	1,831,039
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	694,705	725,995
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	1,151,860	1,207,241
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets
Securities available for sale	1,127,697	812,689
Recurring basis | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Securities available for sale	457,357	500,663
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate securities.
Assets
Securities available for sale	30,160	18,734
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	83,339	65,620
Fair value of Assets, Total	83,339	$ 65,620
Changes in fair value of assets
Fair value of assets at the beginning of the period	65,620
Servicing assets that resulted from transfers of financial assets	7,122
Changes in fair value assets due to valuation inputs or assumptions	12,827
Changes in fair value due to decay	(2,230)
Fair value of assets at the end of the period	83,339
Unrealized losses included in accumulated other comprehensive income related to Level 3 financial assets and liabilities	$ 0