Stockholders' Equity (Narrative) (Details) (USD $)	1 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2012	Jun. 30, 2013	Jun. 30, 2013 Open Market Repurchase Program for Common Stock, Adopted December 14, 2011 [Member]	Jun. 30, 2013 Open Market Repurchase Program for Common Stock, Adopted December 14, 2011 [Member]
Class of Stock [Line Items]
Total capital stock, shares authorized	400,000,000	400,000,000
Common stock, shares authorized	300,000,000	300,000,000
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares outstanding	0	0
Preferred stock, par value per share	$ 0.01	$ 0.01
Common stock, par value per share	$ 0.01	$ 0.01
Maximum number of shares authorized for repurchase			4,000,000	4,000,000
Maximum value of shares authorized under repurchase program				$ 100,000,000
Period repurchase program in force unless maximum dollar amount of repurchases expended first				3 years
Number of shares repurchased and retired			183,000	706,023
Weighted-average price of repurchased and retired shares, per share			$ 45.90	$ 38.39
Common Stock, Dividends, Per Share, Declared	$ 0.25
Dividends, Common Stock	23,000,000
Maximum amount of dividends or stock repurchases permissable under the Credit Facility		150,000,000
Amount available for dividend payments, stock repurchases or Senior Notes repurchases at period end		$ 254,900,000