Employee Retirement and Profit Sharing Plans - Fair Values by Category of Inputs Footnotes (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
U.S. large-cap stocks percentage	90.00%	90.00%
International stocks percentage	10.00%	10.00%

Index Funds Equity Funds Percentage Invested In International Stocks

No definition available.

Name:	df_IndexFundsEquityFundsPercentageInvestedInInternationalStocks
Namespace Prefix:	df_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration