Fair Value Measurements (Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Senior Notes due 2021 at 4.875% [Member]
Senior notes	$ 533,150
Senior Notes due 2021 at 4.875% [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Senior notes	533,150
Senior Notes due 2021 at 4.875% [Member] | Significant Other Observable Inputs (Level 2) [Member]
Senior notes	0
Senior Notes due 2021 at 4.875% [Member] | Significant Unobservable Inputs (Level 3) [Member]
Senior notes	0
Senior Notes due 2021 at 4.625% [Member]
Senior notes	313,830
Senior Notes due 2021 at 4.625% [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Senior notes	313,830
Senior Notes due 2021 at 4.625% [Member] | Significant Other Observable Inputs (Level 2) [Member]
Senior notes	0
Senior Notes due 2021 at 4.625% [Member] | Significant Unobservable Inputs (Level 3) [Member]
Senior notes	$ 0