Employee and Retiree Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended			120 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Future annual rate of increase in cost of health care for 2016 to measure postretirement benefit obligations	6.70%			6.70%
Ultimate rate of health care cost in 2028 and thereafter	4.50%			4.50%
Plan asset, maximum investment in any one issuer	10.00%			10.00%
Equity securities minimum market capitalization	$ 100,000			$ 100,000
Fixed income portfolio, maximum average maturity years	11 years
Weighted average expected return on plan asset	5.64%
Basis used to determine expected return on plan asset, average expected investment expenses	0.60%
Perentage return on plan assets				6.66%
Defined benefit plan, percentage of employer's matching contribution	6.00%
Thrift plan expense	$ 7,800	$ 7,400	$ 7,600
Investment 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Domestic plan, investment notice period	90 days
Investment 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Domestic plan, investment lock up period	2 years
Domestic plan, investment notice period	95 days
Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average expected return on plan asset	7.15%
Defined Benefit Plan, Equity Securities [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	40.00%			40.00%
Defined Benefit Plan, Equity Securities [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	70.00%			70.00%
Defined Benefit Plan, Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average expected return on plan asset	4.26%
Defined Benefit Plan, Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	30.00%			30.00%
Defined Benefit Plan, Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	60.00%			60.00%
Defined Benefit Plan, Long/Short Equity [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	0.00%			0.00%
Defined Benefit Plan, Long/Short Equity [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	15.00%			15.00%
Defined Benefit Plan, Cash And Equivalents [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	0.00%			0.00%
Defined Benefit Plan, Cash And Equivalents [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	15.00%			15.00%
Defined Benefit Plan, Equity Securities, Emerging Market Commingled Equity Fund [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Domestic plan, investment notice period	10 days
Canada [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	60.00%			60.00%
Canada [Member] | Defined Benefit Plan, Equity Securities [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	55.00%			55.00%
Canada [Member] | Defined Benefit Plan, Equity Securities [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	65.00%			65.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	35.00%			35.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	30.00%			30.00%
Canada [Member] | Defined Benefit Plan, Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	40.00%			40.00%
Canada [Member] | Defined Benefit Plan, Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	5.00%			5.00%
Canada [Member] | Defined Benefit Plan, Cash [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	0.00%			0.00%
Canada [Member] | Defined Benefit Plan, Cash [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	10.00%			10.00%
United Kingdom [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target interest and inflation rate hedge ratio	100.00%
United Kingdom [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	60.00%			60.00%
United Kingdom [Member] | Defined Benefit Plan, Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocations of plan assets	40.00%			40.00%
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to benefit plans	$ 24,918	$ 8,186
Weighted average expected return on plan asset	5.64%	5.62%
Pension Benefits [Member] | United States [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to benefit plans	$ 18,000
Expected benefit plan contributions to be made during next year	24,400			$ 24,400
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to benefit plans	6,900
Expected benefit plan contributions to be made during next year	600			600
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to benefit plans	2,417	$ 3,581
Other Postretirement Benefits [Member] | United States [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to benefit plans	2,400
Expected benefit plan contributions to be made during next year	$ 5,400			$ 5,400