Premises and Equipment, Net of Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Premises and Equipment, Net of Accumulated Depreciation
Accumulated depreciation	$ (110,696)	$ (99,409)
Premises and equipment, net	194,030	179,175
Land
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	30,108	27,605
Office buildings and construction in progress
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	187,787	172,544
Furniture, fixtures and equipment
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	78,803	70,622
Leasehold improvements
Premises and Equipment, Net of Accumulated Depreciation
Premises and equipment, gross	$ 8,028	$ 7,813