Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Change in Benefit Obligation, Plan Assets and Funded Status for Company-Sponsored Benefit Plans and Obligations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 292,200
Fair value of plan assets at end of year	289,675	$ 292,200
Amounts recognized in the consolidated balance sheets [Abstract]
Noncurrent liabilities	(123,284)	(119,369)
Pension Plans [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	(382,071)	(417,694)
Service cost	(6,508)	(6,159)	$ (5,081)
Interest cost	(17,020)	(17,012)	(19,184)
Actuarial gain (loss)	(13,997)	27,094
Benefits paid	34,135	31,700
Benefit obligation at end of year	(385,461)	(382,071)	(417,694)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	292,200	337,059
Actual return on plan assets	28,626	(14,970)
Employer contributions and benefit payments	2,984	1,811
Benefits paid	(34,135)	(31,700)
Fair value of plan assets at end of year	289,675	292,200	337,059
Amounts recognized in the consolidated balance sheets [Abstract]
Current liabilities	(1,824)	(1,791)
Noncurrent liabilities	(93,962)	(88,080)
Funded status	(95,786)	(89,871)
Other Postretirement Employee Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	(35,471)	(41,561)
Service cost	(14)	(22)	(25)
Interest cost	(1,421)	(1,456)	(1,741)
Actuarial gain (loss)	(313)	3,778
Benefits paid	3,882	3,790
Benefit obligation at end of year	(33,337)	(35,471)	$ (41,561)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions and benefit payments	3,882	3,790
Benefits paid	(3,882)	(3,790)
Amounts recognized in the consolidated balance sheets [Abstract]
Current liabilities	(4,015)	(4,182)
Noncurrent liabilities	(29,322)	(31,289)
Funded status	$ (33,337)	$ (35,471)