Pension Plans (Obligations and Funded Status) (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]
Fair value of plan assets at beginning of year		$ 553,858
Fair value of plan assets at end of year		572,174		$ 553,858
Noncurrent liabilities		(156,427)		(158,984)
Qualified Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		712,842		738,279
Service cost		4,596		14,131	$ 11,759
Interest cost		24,488		27,514	28,835
Actuarial liability (gain) loss	[1]	20,588		(36,245)
Benefit payments		(33,913)		(30,837)
Projected benefit obligation at end of year		728,601		712,842	738,279
Fair value of plan assets at beginning of year		553,858		596,733
Actual return on plan assets		42,229		(22,038)
Employer contributions		10,000		10,000
Fair value of plan assets at end of year		572,174		553,858	596,733
Funded status at end of year		(156,427)		(158,984)
Accumulated benefit obligation		728,601		712,842
Current liabilities		0	[2]	0
Noncurrent liabilities		(156,427)		(158,984)
Total		(156,427)		(158,984)
Unrecognized (gain) or loss		193,764		187,331
Amount included in accumulated other comprehensive income		193,764		187,331
Qualified pension plan and SERP that will be amortized from accumulated other comprehensive income (loss) in next fiscal year		13,400
SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		10,184		10,349
Service cost		0		206	256
Interest cost		254		318	342
Actuarial liability (gain) loss	[1]	155		(155)
Benefit payments		(534)		(534)
Projected benefit obligation at end of year		10,059		10,184	10,349
Fair value of plan assets at beginning of year		0		0
Actual return on plan assets		0		0
Employer contributions		534		534
Fair value of plan assets at end of year		0		0	$ 0
Funded status at end of year		(10,059)		(10,184)
Accumulated benefit obligation		10,059		10,184
Current liabilities		(3,061)		(530)
Noncurrent liabilities		(6,998)		(9,654)
Total		(10,059)		(10,184)
Unrecognized (gain) or loss		1,209		1,236
Amount included in accumulated other comprehensive income		1,209		$ 1,236
Qualified pension plan and SERP that will be amortized from accumulated other comprehensive income (loss) in next fiscal year		$ 200

[1] The actuarial liability (gain)/loss amount for the qualified pension plan for 2016 and 2015 is principally due to the effect of changes in the discount rate.

[2] (a) The current liabilities are included in other accruals and payables on the Consolidated Balance Sheets