Pension Benefit and Retirement Health and Life Insurance Benefits (Obligations and Funded Status) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in plan assets:
Employer contributions		$ 6,500	$ 13,000
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year		187,882	174,325
Addition of Bear Plan		4,169	0
Service cost		0	0	$ 2,473
Interest cost		7,523	8,015	7,753
Actuarial (gain) loss		(8,674)	34,006
Benefit payments		(8,541)	(24,934)
Plan Amendment		0	0
Special termination benefit	$ (5,200)	0	(3,530)
Benefit obligation at end of year	187,882	182,359	187,882	174,325
Change in plan assets:
Fair value of plan assets at the beginning of the year		170,600	171,218
Addition of Bear Plan		2,171	0
Actual return on plan assets		(194)	10,445
Employer contributions		6,971	13,871
Benefit payments		(8,541)	(24,934)
Fair value of plan assets at the end of the year	170,600	171,007	170,600	171,218
Funded status	(17,282)	(11,352)	(17,282)
Retirement Health and Life Insurance Benefits
Change in benefit obligation:
Benefit obligation at beginning of year		9,839	10,824
Addition of Bear Plan		0	0
Service cost		411	556	627
Interest cost		216	305	262
Actuarial (gain) loss		(1,362)	(1,071)
Benefit payments		(766)	(775)
Plan Amendment		(5,616)	0
Special termination benefit		0	0
Benefit obligation at end of year	9,839	2,722	9,839	10,824
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		766	775
Benefit payments		(766)	(775)
Fair value of plan assets at the end of the year	0	0	0	$ 0
Funded status	$ (9,839)	$ (2,722)	$ (9,839)