Stockholders' Equity (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2011	Jun. 30, 2013	Jun. 30, 2012
Class of Stock [Line Items]
Allocated Share-based Compensation Expense	$ 2,687,000	$ 2,213,000		$ 5,613,000	$ 4,420,000
Treasury Stock, Shares, Acquired		505,137	0
Treasury Stock Acquired, Average Cost Per Share		$ 13.98		$ 15.37
Shares Repurchased to date				5,853,975
2008 Repurchase Program [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				90,000,000
2012 Repurchase Program [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				50,000,000
Performance Shares [Member]
Class of Stock [Line Items]
Allocated Share-based Compensation Expense	$ 400,000	$ 300,000		$ 800,000	$ 500,000