FAIR VALUE MEASUREMENTS (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Auction rate securities	$ 4,352,000			$ 4,352,000			$ 4,354,000
Marketable securities	11,787,000			11,787,000			11,778,000
Temporary decline in fair value of securities	(300,000)			(300,000)
Changes in the entity's auction rate securities measured at fair value on a recurring basis using significant unobservable inputs (Level 3)
Unrealized gain (loss) included in other comprehensive income - less than $0.1m for six months ended 2013				(100,000)		100,000
Fair Value, Measurements, Recurring [Member] | Total
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Auction rate securities	4,352,000	[1]		4,352,000	[1]		4,354,000	[1]
Derivative Assets	60,000	[2]		60,000	[2]		165,000	[2]
Marketable securities	11,787,000	[3]		11,787,000	[3]		11,778,000	[3]
Derivative Liabilities	239,000	[2]		239,000	[2]		1,242,000	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Auction rate securities		[1]			[1]			[1]
Derivative Assets		[2]			[2]		0	[2]
Marketable securities	11,787,000	[3]		11,787,000	[3]		11,778,000	[3]
Derivative Liabilities	0	[2]		0	[2]		0	[2]
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Auction rate securities		[1]			[1]			[1]
Derivative Assets	60,000	[2]		60,000	[2]		165,000	[2]
Marketable securities		[3]			[3]			[3]
Derivative Liabilities	239,000	[2]		239,000	[2]		1,242,000	[2]
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Auction rate securities	4,352,000	[1]		4,352,000	[1]		4,354,000	[1]
Derivative Assets	0	[2]		0	[2]		0	[2]
Marketable securities		[3]			[3]			[3]
Derivative Liabilities	0	[2]		0	[2]		0	[2]
Changes in the entity's auction rate securities measured at fair value on a recurring basis using significant unobservable inputs (Level 3)
Balance at the beginning of the period	4,352,000		4,326,000	4,354,000		4,245,000
Unrealized gain (loss) included in other comprehensive income - less than $0.1m for six months ended 2013	0		0	(2,000)		81,000
Balance at the end of the period	4,352,000		4,326,000	4,352,000		4,326,000
Unsecured Debt [Member] | Unsecured Senior Notes 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt, Fair Value	780,900,000			780,900,000			816,000,000
Unsecured Debt [Member] | Unsecured Senior Notes 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt, Fair Value	$ 573,100,000			$ 573,100,000			$ 623,500,000

[1] The auction rate securities are classified as available-for-sale and the fair value of these securities was estimated utilizing a probability discounted cash flow analysis. As of September 30, 2013, all of the Company's auction rate securities continue to have AAA underlying ratings. The Company attributes the $0.3 million decline in the fair value of the securities from the original cost basis to external liquidity issues rather than credit issues. The Company assessed the decline in value to be temporary because it does not intend to sell and it is more likely than not that the Company will not have to sell the securities before their maturity. During the nine months ended September 30, 2013 and 2012, the Company recorded an unrealized pre-tax loss of less than $0.1 million and a pre-tax gain of $0.1 million, respectively, on its auction rate securities.

[2] The fair value of derivatives is recorded based on the present value of cash flows using a crude oil forward rate curve.

[3] The fair value of marketable securities is recorded based on quoted market prices and changes in fair value were included in other comprehensive income.