CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Net Cash Provided by Operating Activities	$ 47,184	$ 51,301
Cash Flows from Investing Activities:
Capital Expenditures	(77,548)	(55,611)
Net Sale of Restricted Investments in Margin Accounts	458	994
Investment in Long-Term Receivables	(2,871)	(2,390)
Proceeds from Long-Term Receivables	3,781	2,418
Net Cash Used in Investing Activities	(76,180)	(54,589)
Cash Flows from Financing Activities:
Net Borrowing from Short-Term Credit Facilities	26,900	1,600
Proceeds from Issuance of Long-Term Debt	35,000	0
Principal Repayments of Long-Term Debt	(35,000)	0
Premium for Early Retirement of Debt	(700)	0
Payments for Issuance of Long-Term Debt	(341)	(28)
Net Cash Provided by Financing Activities	25,859	1,572
Net Decrease in Cash and Cash Equivalents	(3,137)	(1,716)
Cash and Cash Equivalents at Beginning of Period	3,504	2,030
Cash and Cash Equivalents at End of Period	$ 367	$ 314