Stockholders' Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity [Abstract]
Unrecognized prior service cost and net actuarial (losses) on pension plans	$ (15,284)	$ (18,227)	$ (21,557)
Unrealized gains on derivatives (cash flow hedges)	2,144	1,772	0
Unrealized net holding (losses) on AFS securities	(8,937)	(5,065)	(861)
Accumulated other comprehensive (loss)	$ (22,077)	$ (21,520)	$ (22,418)
Class of Warrant or Right [Line Items]
Preceding period of retained net profits for approval of Office of Comptroller of the Currency	2 years
Statutory amount available for dividend payments	$ 107,500
Common stock repurchased during period (in shares)	0	675,535	1,047,152
Number of shares available for repurchase under stock repurchase program (in shares)	1,000,000