Premises and Equipment, Net - Premises and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 896,790	$ 988,968
Accumulated depreciation and amortization	(426,659)	(455,830)
Premises and equipment, net	470,131	533,138
Depreciation and amortization expense	76,000	75,300	$ 48,600
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	131,712	151,332
Office buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	303,712	334,673
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	56,687	59,141
Furniture, equipment and computer software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	401,494	440,642
Premises and equipment leased under finance leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,185	3,180
Premises and equipment, net	$ 326,900	$ 289,700