Fair Value - Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Assets
Derivative financial instruments	$ 966,000	$ 14,600
Trading securities	494
Securities available for sale	3,137,718	1,717,276	$ 1,956,047
Liabilities
Derivative financial instruments	970,000	15,800
Government-sponsored entities debt
Assets
Securities available for sale	4,913	66,529	25,941
U.S. Treasuries
Assets
Securities available for sale	199,987
State and municipal obligations
Assets
Securities available for sale	453,654	182,146	208,415
Corporate securities.
Assets
Securities available for sale	5,695
Significant Other Observable Inputs (Level 2)
Assets
Loans held for sale		47,796
Trading securities	494
Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	25,441	30,332	30,525
Changes in fair value of assets
Changes in hierarchy classifications of Level 3 liabilities	0
Recurring basis
Assets
Derivative financial instruments	978,257	17,587	16,252
Loans held for sale	603,275	47,796	59,363
Trading securities	494
Securities available for sale	3,137,718	1,717,276	1,956,047
Mortgage servicing rights	25,441	30,332	30,525
Fair value of Assets, Total	4,745,185	1,812,991	2,062,187
Liabilities
Derivative financial instruments	1,017,933	30,286	31,273
Recurring basis | Government-sponsored entities debt
Assets
Securities available for sale	4,913	66,529	25,941
Recurring basis | U.S. Treasuries
Assets
Securities available for sale	199,987
Recurring basis | State and municipal obligations
Assets
Securities available for sale	453,654	182,146	208,415
Recurring basis | Mortgage-backed securities
Assets
Securities available for sale	2,473,469	1,468,601	1,721,691
Recurring basis | Corporate securities.
Assets
Securities available for sale	5,695
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	978,257	17,587	16,252
Loans held for sale	603,275	47,796	59,363
Trading securities	494
Securities available for sale	3,137,718	1,717,276	1,956,047
Fair value of Assets, Total	4,719,744	1,782,659	2,031,662
Liabilities
Derivative financial instruments	1,017,933	30,286	31,273
Recurring basis | Significant Other Observable Inputs (Level 2) | Government-sponsored entities debt
Assets
Securities available for sale	4,913	66,529	25,941
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Treasuries
Assets
Securities available for sale	199,987
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets
Securities available for sale	453,654	182,146	208,415
Recurring basis | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Securities available for sale	2,473,469	1,468,601	1,721,691
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate securities.
Assets
Securities available for sale	5,695
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	25,441	30,332	30,525
Fair value of Assets, Total	25,441	30,332	$ 30,525
Changes in fair value of assets
Fair value of assets at the beginning of the period	30,525	34,727
Servicing assets that resulted from transfers of financial assets	8,211	2,558
Changes in fair value assets due to valuation inputs or assumptions	(10,097)	(4,924)
Changes in fair value due to decay	3,198	2,029
Fair value of assets at the end of the period	25,441	30,332
Unrealized losses included in accumulated other comprehensive income related to Level 3 financial assets and liabilities	0	$ 0
Recurring basis | Significant Unobservable Inputs (Level 3) | CSFL
Changes in fair value of assets
Servicing assets that resulted from transfers of financial assets	$ 3,200