Shareholders' Equity (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended
	Jun. 30, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2009 5.125% convertible senior notes, due 2014	Jun. 29, 2009 5.125% convertible senior notes, due 2014	Jun. 29, 2009 Term A loan
Common Stock Issuance
Public offering (in shares)	31,050,000
Public offering price per share (in dollars per share)	$ 13.50
Proceeds from issuance of common stock and convertible senior notes					$ 678,800,000
Stated interest rate on convertible senior notes						5.125%
Outstanding Term A loan							552,000,000
Cash dividends
Cash dividend declared		87,452,000	65,087,000	66,690,000
Cash dividend declared per share (in dollars per share)		$ 0.400	$ 0.300	$ 0.325
Cash dividend paid		$ 81,882,000	$ 64,969,000	$ 68,672,000
Treasury Stock
Remaining authorization to repurchase treasury stock (in shares)		3,600,000