Fair Value Measurements (Carrying Amount and Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash		$ 8,542
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	22,938	53,583
Restricted cash		8,542
Credit facility	282,900
Senior notes	1,668,396	1,669,473
Derivative instruments, net	38,013	287,878
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	22,938	53,583
Restricted cash		8,542
Credit facility	282,900
Senior notes	1,795,935	1,917,005
Derivative instruments, net	$ 38,013	$ 287,878