Premises and Equipment, Net of Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Premises and Equipment, Net of Accumulated Depreciation
Accumulated depreciation	$ (137,237)	$ (127,876)
Premises and equipment, net	241,528	177,348
Land
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	47,511	31,370
Buildings and construction in progress
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	231,854	182,592
Furniture, fixtures and equipment
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	90,030	83,177
Leasehold improvements
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	$ 9,370	$ 8,085