Pension Benefit and Retirement Health and Life Insurance Benefits (Obligations and Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in plan assets:
Employer contributions		$ 6,500
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 182,359	187,882
Addition of Bear Plan	0	4,169
Service cost	0	0	$ 0
Interest cost	7,530	7,523	8,015
Actuarial (gain) loss	(3,621)	(8,674)
Benefit payments	(8,572)	(8,541)
Plan Amendment	0	0
Benefit obligation at end of year	177,696	182,359	187,882
Change in plan assets:
Fair value of plan assets at the beginning of the year	171,007	170,600
Addition of Bear Plan	0	2,171
Actual return on plan assets	8,999	(194)
Employer contributions	344	6,971
Benefit payments	(8,572)	(8,541)
Fair value of plan assets at the end of the year	171,778	171,007	170,600
Unfunded status	(5,918)	(11,352)
Retirement Health and Life Insurance Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	2,722	9,839
Addition of Bear Plan	0	0
Service cost	133	411	556
Interest cost	75	216	305
Actuarial (gain) loss	72	(1,362)
Benefit payments	(860)	(766)
Plan Amendment	0	(5,616)
Benefit obligation at end of year	2,142	2,722	9,839
Change in plan assets:
Fair value of plan assets at the beginning of the year	0	0
Addition of Bear Plan	0	0
Actual return on plan assets	0	0
Employer contributions	860	766
Benefit payments	(860)	(766)
Fair value of plan assets at the end of the year	0	0	$ 0
Unfunded status	$ (2,142)	$ (2,722)