Premises and Equipment, Net - Summary of Premises and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 1,013,236	$ 873,040
Less: Accumulated depreciation and amortization	(459,042)	(445,506)
Premises and equipment, net	554,194	427,534
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	156,380	144,754
Office buildings
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	345,663	268,495
Leasehold improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	57,274	51,868
Furniture, equipment and computer software
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	450,739	404,743
Premises and equipment leased under capital leases
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	3,180	$ 3,180
Premises and equipment, net	$ 285,400