Fair Value Measurements (Narrative) (Details) $ in Thousands, lb in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) property lb $ / lb	Dec. 31, 2015 USD ($) property	Dec. 31, 2014 USD ($) property
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Deferred Compensation, Percentage Of Funds Invested	60.00%
Number of years long-term sales growth forecasted over	6 years
Average long-term sales growth forecast, over next 4 years, percent per year	14.00%
Derivative nonmonetary notional amount, mass | lb	40.8
Underlying derivative mass | $ / lb	0.25
Derivative asset	$ 2,300
Combined carrying value	$ 172,748	$ 150,600
Vacant Owned Facilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Number of vacant owned properties | property	1	3	4
Number properties classified as fixed assets | property	1	1	3
Number of vacant owned facilities sold | property		1
Number of vacant facilities reopened | property		1
Estimated combined fair value	$ 3,000
Combined carrying value	$ 2,500
Vacant Owned Facilities Classified in Fixed Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Estimated combined fair value		$ 3,000	$ 4,200
Combined carrying value		$ 2,500	$ 3,900