Fair Value - Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Assets
Derivative financial instruments	$ 480,600	$ 802,800
Securities available for sale	4,631,554	3,330,672
Liabilities
Derivative financial instruments	480,600	802,700
Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	1,630,448	1,367,132
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	999,288	240,108
State and municipal obligations
Assets
Securities available for sale	729,602	520,039
Corporate securities.
Assets
Securities available for sale	13,845	13,702
Significant Other Observable Inputs (Level 2)
Assets
Loans held for sale	242,813	290,467
Trading securities	61,294	10,674
Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	60,922	43,820
Changes in fair value of assets
Fair value of assets at the beginning of the period	43,820
Servicing assets that resulted from transfers of financial assets	20,835
Changes in fair value assets due to valuation inputs or assumptions	3,653
Changes in fair value due to decay	(7,386)
Fair value of assets at the end of the period	60,922
Changes in hierarchy classifications of Level 3 liabilities	0
Recurring basis
Assets
Derivative financial instruments	489,085	813,899
Loans held for sale	242,813	290,467
Trading securities	61,294	10,674
Securities available for sale	4,631,554	3,330,672
Mortgage servicing rights	60,922	43,820
Fair value of Assets, Total	5,485,668	4,489,532
Liabilities
Derivative financial instruments	485,007	804,832
Recurring basis | Government-sponsored entities debt
Assets
Securities available for sale	72,843	29,256
Recurring basis | Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	1,630,448	1,367,132
Recurring basis | Residential Collateralized Mortgage-Obligations Issued By U.S. Government Agencies Or Sponsored Enterprises [Member]
Assets
Securities available for sale	708,128	755,551
Recurring basis | Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Assets
Securities available for sale	999,288	240,108
Recurring basis | State and municipal obligations
Assets
Securities available for sale	729,602	520,039
Recurring basis | Mortgage-backed securities
Assets
Securities available for sale	477,400	404,884
Recurring basis | Corporate securities.
Assets
Securities available for sale	13,845	13,702
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	489,085	813,899
Loans held for sale	242,813	290,467
Trading securities	61,294	10,674
Securities available for sale	4,631,554	3,330,672
Fair value of Assets, Total	5,424,746	4,445,712
Liabilities
Derivative financial instruments	485,007	804,832
Recurring basis | Significant Other Observable Inputs (Level 2) | Government-sponsored entities debt
Assets
Securities available for sale	72,843	29,256
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	1,630,448	1,367,132
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	708,128	755,551
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	999,288	240,108
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets
Securities available for sale	729,602	520,039
Recurring basis | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Securities available for sale	477,400	404,884
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate securities.
Assets
Securities available for sale	13,845	13,702
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	60,922	43,820
Fair value of Assets, Total	60,922	$ 43,820
Changes in fair value of assets
Unrealized losses included in accumulated other comprehensive income related to Level 3 financial assets and liabilities	$ 0