Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Apr. 30, 2012
Financial Assets (Liabilities):
Derivative instruments - liabilities	$ (8,506)	$ (389)
Notes 5.875 Percent [Member]
Financial Assets (Liabilities):
Interest rate (as a percent)	5.875%	5.875%	5.875%
Notes 5.875 Percent [Member] | Fair Value Inputs Level1 [Member]
Financial Assets (Liabilities):
Interest rate (as a percent)	5.875%
Notes 4.375 Percent [Member]
Financial Assets (Liabilities):
Interest rate (as a percent)	4.375%
Notes 4.375 Percent [Member] | Fair Value Inputs Level1 [Member]
Financial Assets (Liabilities):
Interest rate (as a percent)	4.375%
Carrying Reported Amount Fair Value Disclosure [Member]
Financial Assets (Liabilities):
Derivative instruments - assets		4,268
Derivative instruments - liabilities	(8,506)	(389)
Carrying Reported Amount Fair Value Disclosure [Member] | Notes 5.875 Percent [Member]
Financial Assets (Liabilities):
Long-term debt	(750,000)	(750,000)
Carrying Reported Amount Fair Value Disclosure [Member] | Line Of Credit [Member]
Financial Assets (Liabilities):
Long-term debt		(174,000)
Carrying Reported Amount Fair Value Disclosure [Member] | Notes 4.375 Percent [Member]
Financial Assets (Liabilities):
Long-term debt	(750,000)
Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Assets (Liabilities):
Derivative instruments - assets		4,268
Derivative instruments - liabilities	(8,506)	(389)
Estimate Of Fair Value Fair Value Disclosure [Member] | Notes 5.875 Percent [Member]
Financial Assets (Liabilities):
Long-term debt	(832,500)	(799,988)
Estimate Of Fair Value Fair Value Disclosure [Member] | Line Of Credit [Member]
Financial Assets (Liabilities):
Long-term debt		(174,000)
Estimate Of Fair Value Fair Value Disclosure [Member] | Notes 4.375 Percent [Member]
Financial Assets (Liabilities):
Long-term debt	$ (765,938)