Premises and Equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) floor	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Premises and equipment
Premises and equipment, gross	$ 194,909	$ 210,210
Less: accumulated depreciation and amortization	140,949	150,877
Total	53,960	59,333
Depreciation and amortization expense	18,300	16,500	$ 16,300
Reduction in premises and equipment costs	30,600
Reduction in accumulated depreciation and amortization	10,200
Written off of leasehold assets	$ 7,492
Number of leasehold floors available before write off | floor	3
Number of floors available after written off | floor	2
Furniture, fixtures and equipment
Premises and equipment
Premises and equipment, gross	$ 149,366	157,770
Leasehold improvements
Premises and equipment
Premises and equipment, gross	$ 45,543	$ 52,440