Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) mutual_fund	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Minimum percentages of gain loss consider for amortization (in hundredths)	10.00%
Minimum value of outstanding noncallable bonds used in hypothetical cash flow bond matching exercise	$ 50,000,000
Future earnings period used in determining the expected average rate of earnings	20 years
Discretionary profit sharing contribution as a percentage of participant's eligible compensation (in hundredths)	5.00%
Minimum percentage return should exceed growth in consumer price index annually (in hundredths)	5.75%
Maximum investment in international oriented funds (in hundredths)	30.00%
Number of international mutual funds | mutual_fund	2
Percent of international oriented funds equity allocation in emerging markets (in hundredths)	3.00%
Percent of international oriented funds equity allocation in companies based outside of the United States, primarily Europe and the Pacific Basin (in hundredths)	21.00%
Matching contribution rate on employees' before-tax contributions, first contribution level (in hundredths)	80.00%
Employee contributions subject to employer match, first contribution level	$ 1,000
Matching contribution rate on employees' before-tax contributions, second contribution level (in hundredths)	40.00%
Employee contributions subject to employer match, second contribution level	$ 2,000
Matching contribution rate on employees' before-tax contributions, hired after 01/01/2014 (in hundredths)	100.00%
Employee contributions subject to employer match for employees hired after 01/01/2014 (in hundredths)	4.00%
Profit sharing and 401(k) savings plan expenses	$ 5,100,000	$ 5,000,000	$ 5,300,000
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Lump sum pension plan benefit payments	$ 22,400,000	11,800,000
Total increase in benefit obligation using new mortality tables		23,200,000
Percentage of participants electing lump sum payments (in hundredths)	75.00%
Increase in benefit obligation using new mortality tables and lump sum election assumption		$ 14,600,000
Pension Plan | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations, maximum (in hundredths)	40.00%
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Age of retirees at which retirement benefits under the plan are terminated	65 years
Health care trend rate used for pre-65 benefits (in hundredths)	7.00%
Health care trend rate used for pre-65 benefits in 2016 (in hundredths)	7.00%
Health care trend rate used for pre-65 benefits in 2020 (in hundredths)	5.00%
Other Postretirement Benefit Plan | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations, maximum (in hundredths)	100.00%