Fair Value Measurements (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 18,719	$ 22,938
Credit facility	160,200	282,900
Senior notes	1,668,426	1,668,396
Derivative instruments, net	(72,225)	38,013
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	18,719	22,938
Credit facility	160,200	282,900
Senior notes	1,825,949	1,795,935
Derivative instruments, net	$ (72,225)	$ 38,013