Disclosure of Fair Value of Financial Instruments Disclosure of Fair Value of Financial Instruments - Level 3 Rollforward (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Discount Rate	2.89%		2.87%
Long-tern Debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Long-term debt at December 31, 2012 (1)	2,841,917	[1]
Payoffs and amortization of long-term debt (1)	(1,249)	[1]
New long-term debt (1)	3,456	[1]
Changes in fair value assumptions (1)	(24,330)	[1]
Long-term debt at March 31, 2013 (1)	2,819,794	[1]
Carrying Value of Debt to be Fair Valued [Roll Forward]
Long-term debt at December 31, 2012 (1)	2,561,606	[1]
Payoffs and amortization of long-term debt (1)	(1,249)	[1]
New long-term debt (1)	3,456	[1]
Long-term debt at March 31, 2013 (1)	2,563,813	[1]
Fair Value Above (Below) Carrying Value [Roll Forward]
Long-term debt at December 31, 2012 (1)	280,311	[1]
Changes in fair value assumptions (1)	(24,330)	[1]
Long-term debt at March 31, 2013 (1)	255,981	[1]

[1] Does not include the Company's credit facility.