CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Statement of Cash Flows [Abstract]
Net Cash Provided by Operating Activities	$ 109,974	$ 51,006
Cash Flows from Investing Activities:
Capital Expenditures	(118,383)	(114,886)
Net (Purchase) Sale of Restricted Investments in Margin Accounts	(809)	641
Investment in Long-Term Receivables	(5,012)	(4,178)
Proceeds from Long-Term Receivables	5,376	5,217
Net Cash Used in Investing Activities	(118,828)	(113,206)
Cash Flows from Financing Activities:
Net Borrowing from Short-Term Credit Facilities	7,900	11,300
Proceeds from Issuance of Long-Term Debt	0	85,000
Principal Repayments of Long-Term Debt	(25,000)	(35,000)
Premium for Early Retirement of Debt	0	(700)
Payments for Issuance of Long-Term Debt	(30)	(936)
Additional Investment by Shareholder	25,000	0
Net Cash Provided by Financing Activities	7,870	59,664
Net Decrease in Cash and Cash Equivalents	(984)	(2,536)
Cash and Cash Equivalents at Beginning of Period	2,678	3,504
Cash and Cash Equivalents at End of Period	$ 1,694	$ 968