Other Postretirement Benefits (Changes in the Accumulated Postretirement Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at	$ 1,685	$ 1,961	$ 2,179
Interest cost	59	66	88
Actuarial losses (gains)	5	(39)	9
Benefits paid	(372)	(303)	(315)
Projected benefit obligation at	1,377	1,685	1,961
Fair value of plan assets	0	0	0
Under funded status	(1,377)	(1,685)	(1,961)
Unamortized prior service cost	4	10	24
Unrecognized actuarial gain	(200)	(218)	(179)
Net amount recognized	(1,573)	(1,893)	(2,116)
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at	8,149	8,202	5,900
Service cost	22	26	16
Interest cost	272	300	255
Actuarial losses (gains)	(923)	(29)	2,387
Benefits paid	(318)	(350)	(356)
Projected benefit obligation at	7,202	8,149	8,202
Fair value of plan assets	0	0	0
Under funded status	(7,202)	(8,149)	(8,202)
Unamortized prior service cost	471	515	559
Unrecognized actuarial gain	2,679	3,736	3,962
Net amount recognized	$ (4,052)	$ (3,898)	$ (3,681)