Employee Benefit Plans (Consolidated Net Periodic Benefit Costs) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($) Employee	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of Employees Receiving USW Settlement | Employee			11
Pension Plan [Member]
Components of net periodic pension and postretirement benefit expense:
Service cost	$ 18,890		$ 13,400	$ 13,901
Interest cost	7,754		6,675	5,368
Expected return on plan assets	(8,037)		(6,363)	(6,228)
Amortization of prior service cost (credit)	0		33	307
Amortization of net actuarial loss	6,306		3,071	4,334
Settlement	0	[1]	1,809	0
Net periodic expense (credit)	24,913		18,625	17,682
Other Postretirement Benefits [Member]
Components of net periodic pension and postretirement benefit expense:
Service cost	243		227	288
Interest cost	438		506	412
Expected return on plan assets	0		0	0
Amortization of prior service cost (credit)	(3,713)		(3,713)	(3,712)
Amortization of net actuarial loss	885		915	1,035
Settlement	0		0	0
Net periodic expense (credit)	$ (2,147)		$ (2,065)	$ (1,977)

[1] Eleven participants took a lump sum distribution from the USW plan in 2014, resulting in a pension settlement cost of $1.8 million.