Premises and Equipment - Net of Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Premises and Equipment, Net of Accumulated Depreciation
Accumulated depreciation	$ (159,555)	$ (148,373)
Net premises and equipment, excluding ROU assets	272,789	263,236
ROU assets	52,546	47,073
Net premises and equipment	325,335	310,309
Land
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	56,842	52,738
Buildings and construction in progress
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	259,389	251,151
Furniture, Fixtures and Equipment
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	102,749	96,576
Leasehold improvements
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	$ 13,364	$ 11,144