Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Apr. 30, 2012
5.875% Notes due 2022
Financial Assets (Liabilities):
Interest rate (as a percent)	5.875%	5.875%	5.875%
5.875% Notes due 2022 | Level 1
Financial Assets (Liabilities):
Interest rate (as a percent)	5.875%	5.875%
Carrying Amount
Financial Assets (Liabilities):
Derivative instruments - assets	$ 10,351
Derivative instruments - liabilities	(59)
Carrying Amount | 5.875% Notes due 2022
Financial Assets (Liabilities):
Long-term debt	(750,000)	(750,000)
Carrying Amount | Bank debt
Financial Assets (Liabilities):
Long-term debt	(142,000)
Fair Value
Financial Assets (Liabilities):
Derivative instruments - assets	10,351
Derivative instruments - liabilities	(59)
Fair Value | 5.875% Notes due 2022
Financial Assets (Liabilities):
Long-term debt	(780,000)	(825,750)
Fair Value | Bank debt
Financial Assets (Liabilities):
Long-term debt	$ (142,000)