Employee Benefit Plans (Schedule of Net Funded Status) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	$ 40,989	$ 40,989
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance		47,216	$ 40,989
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Beginning Balance	41,086	41,086	39,416
Defined Benefit Plan, Service Cost		278	305
Defined Benefit Plan, Interest Cost		1,650	1,740
Defined Benefit Plan, Other Changes		3,285	3,127
Defined Benefit Plan, Actuarial Gain (Loss)		450	149
Defined Benefit Plan, Settlement Losses		0	(268)
Defined Benefit Plan, Benefits Paid		(1,774)	(3,383)
Defined Benefit Plan, Benefit Obligation, Ending Balance		44,975	41,086
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	40,989	40,989	39,200
Defined Benefit Plan, Actual Return on Plan Assets		5,001	2,172
Defined Benefit Plan, Contributions by Employer	3,000	3,000	3,000
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance		47,216	40,989
Defined Benefit Plan, Unfunded Status of Plan		2,241	(97)
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Beginning Balance	7,302	7,302	6,289
Defined Benefit Plan, Service Cost		113	100
Defined Benefit Plan, Interest Cost		293	279
Defined Benefit Plan, Other Changes		0	0
Defined Benefit Plan, Actuarial Gain (Loss)		112	775
Defined Benefit Plan, Settlement Losses		0	0
Defined Benefit Plan, Benefits Paid		(207)	(141)
Defined Benefit Plan, Benefit Obligation, Ending Balance		7,613	7,302
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	$ 0	0	0
Defined Benefit Plan, Actual Return on Plan Assets		0	0
Defined Benefit Plan, Contributions by Employer		207	141
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance		0	0
Defined Benefit Plan, Unfunded Status of Plan		$ (7,613)	$ (7,302)