Long-Term Debt (Senior Notes) (Details) (USD $)	6 Months Ended	0 Months Ended
	Jun. 30, 2013	Jan. 14, 2011 Senior Notes due 2021 at 4.875% [Member] D	Sep. 19, 2011 Senior Notes due 2021 at 4.625% [Member] D	Aug. 21, 2012 Senior Notes due 2022 at 3.800% [Member] D	Jun. 20, 2013 Senior Notes due 2023 at 3.850% [Member] D
Debt instrument offering date		Jan. 14, 2011	Sep. 19, 2011	Aug. 21, 2012	Jun. 20, 2013
Face amount of senior notes		$ 500,000,000	$ 300,000,000	$ 300,000,000	$ 300,000,000
Interest rate of notes		4.875%	4.625%	3.80%	3.85%
Percentage of face value of debt instrument pricing		99.297%	99.826%	99.627%	99.992%
Number of days in annual interest calculation period		360	360	360	360
Debt instrument covenant compliance	Each of the senior notes is subject to certain customary covenants, with which the Company complied as of June 30, 2013.