Pension Benefits and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,872,000	$ 1,846,000	$ 5,658,000	$ 5,523,000
Expected return on plan assets	(2,698,000)	(2,772,000)	(8,110,000)	(8,314,000)
Amortization of net loss (gain)	445,000	432,000	1,339,000	1,258,000
Net periodic (benefit) cost	(381,000)	(494,000)	(1,113,000)	(1,533,000)
Retirement Health and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	37,000	150,000	111,000	450,000
Interest cost	19,000	75,000	57,000	225,000
Amortization of prior service cost (credit)	(373,000)	0	(1,119,000)
Amortization of net loss (gain)	(19,000)		(57,000)
Net periodic (benefit) cost	(336,000)	225,000	(1,008,000)	675,000
Non-Qualified Defined Benefit Pension Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer			0	6,500,000
Bear Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, required employer contribution	$ 100,000		$ 300,000
Pension and Other Postretirement Benefit Contributions		$ 0		$ 0
Scenario, Forecast | Bear Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, liabilities					$ 300,000