Restructuring Charges (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net	$ 7,000	$ 7,014	$ 8,267	$ 36
Special and contractual termination benefits		6,100
Severance benefits		336
Asset impairment charges		715	8,107	229
Gain on sale of certain branch locations				401
Other operating expenses		88,949	92,919	91,370
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		$ 6,100
Continued Corporate Real Estate Optimization Activities
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net			5,300
Facility Closing
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net			$ 2,800
Other operating expenses				$ 437