Premises and Equipment, Net - Premises and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 144,754	$ 146,688
Office buildings	268,495	272,428
Leasehold improvements	51,868	48,543
Furniture, equipment and computer software	404,743	363,445
Premises and equipment leased under capital leases	3,180	0
Subtotal	873,040	831,104
Less: Accumulated depreciation and amortization	445,506	409,555
Premises and equipment, net	427,534	421,549
Depreciation, Depletion and Amortization
Depreciation and amortization expense	48,600	45,900	$ 44,900
Operating leases
Lease expense	38,000	36,400	36,500
Sublease income	1,000	$ 1,000	$ 1,000
Future minimum rental payments for operating leases
2019	26,309
2020	25,160
2021	17,144
2022	12,258
2023	10,590
Thereafter	32,448
Total	$ 123,909