Fair Value Measurements (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 Contract	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of bonds received	2
Fair Value Measurements (Textual) [Abstract]
Total Debt	$ 1,061,945,000	$ 1,073,825,000
Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis [Abstract]
Deferred compensation plan investments	15,837,000	13,892,000
Total assets measured at fair value	15,837,000	13,892,000
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis [Abstract]
Deferred compensation plan investments	15,837,000	13,892,000
Total assets measured at fair value	15,837,000	13,892,000
Convertible Notes Payable [Member]
Fair Value Measurements (Textual) [Abstract]
Total Debt	322,553,000	319,246,000
Face amount of outstanding debt	360,000,000
Accrued interest on convertible notes	3.75%
Fair value of the convertible notes	332,000,000
Senior Notes [Member]
Fair Value Measurements (Textual) [Abstract]
Total Debt	152,180,000	152,180,000
Accrued interest on convertible notes	6.75%
Fair value of senior notes	149,900,000
Bonds Series A and Series B [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of bonds received	2
Bonds A Series [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivables, carrying value	90,600,000
Maturity date of notes receivable	Jul. 01, 2034
Bonds B Series [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivables, carrying value	58,700,000
Maturity date of notes receivable	Sep. 01, 2037
Notes receivable, fair value	$ 37,000,000