Other Employee Benefit Plans (Narrative) (Details)			12 Months Ended
	Jan. 01, 2016	Sep. 30, 2014	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 01, 2014 year
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Matching contribution (as a percent)				6.00%
Additional matching contribution (as a percent)					3.00%
Age for additional match contribution, maximum | year						40
Years of service for additional match contribution, maximum		10 years
Discretionary contribution to plan			$ 0	$ 9,499,000	$ 0
Payments and costs of plan			$ 9,888,000	17,687,000	13,729,000
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discretionary matching contribution (as a percent)	1.00%		1.00%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discretionary matching contribution (as a percent)	4.00%		6.00%
Retiree Health Benefit Act of 1992
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions to multi-employer plan			$ 7,647,000	8,455,000	9,239,000
Combined fund obligation			82,501,000
Multiemployer Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Letters of credit outstanding			20,983,000	19,170,000	$ 21,473,000
Long-Term Disability
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Combined total obligation			$ 15,315,000	$ 17,421,000