Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivative instruments liabilities [Member]

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Insurance contract

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

^[1]

^[2]

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2)

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

93,657,000

101,443,000

Liabilities:

7,483,000

6,255,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Commodity derivative instruments liabilities [Member]

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

7,483,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Interest rate derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

6,255,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Money market funds

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

19,227,000

24,240,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Insurance contract

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

62,370,000

^[1]

48,898,000

^[2]

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

8,193,000

8,195,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | U.S. Treasury securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

1,917,000

1,806,000

Fair value, measurements, recurring [Member] | Significant Other Observable Inputs (Level 2) | Commodity derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

1,950,000

18,304,000

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3)

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Liabilities:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Commodity derivative instruments liabilities [Member]

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Interest rate derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Liabilities:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Money market funds

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Insurance contract

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

^[1]

^[2]

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | U.S. Treasury securities

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

Fair value, measurements, recurring [Member] | Significant Unobservable Inputs (Level 3) | Commodity derivative instruments

Fair value, assets and liabilities measured on recurring and nonrecurring basis [Line Items]

Assets:

$ 0

[1]	The insurance contract invests approximately 29 percent in common stock of mid-cap companies, 28 percent in common stock of small-cap companies, 28 percent in common stock of large-cap companies and 15 percent in fixed-income investments.
[2]	The insurance contract invests approximately 28 percent in common stock of mid-cap companies, 28 percent in common stock of small-cap companies, 29 percent in common stock of large-cap companies and 15 percent in fixed-income investments.