Combined Balance Sheet and Income Statement Data for Equity Method Investments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
BALANCE SHEET DATA:
Current assets	$ 24,338	[1]	$ 30,905
Noncurrent assets	62,305	[1]	206,076
Total assets	86,643	[1]	236,981
Current liabilities	17,531	[1]	34,825
Other liabilities	23,507	[1]	9,111
Combined equity	45,605	[1]	193,045
Total liabilities and combined equity	86,643	[1]	236,981
INCOME STATEMENT DATA:
Revenue	100,931	[1]	139,355	134,786
Costs and expenses	53,596	[1]	79,584	67,694
Non-operating expense	13,708	[1]	12,290	12,914
Net income	$ 33,627	[1]	$ 47,481	$ 54,178

[1] In May 2011, we sold our 20.0% interest in WT LPG; therefore, the respective balance sheet data is not presented, however the income statement data includes activity through the sale. See Note 3 for further information.