Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jan. 31, 2011
Shareholders' Equity
Number of shares authorized to be repurchased under the current open-market stock repurchase program (in shares)					20,000,000
Repurchase of stock program, period (in years)	3		3
Number of shares repurchased under the current open-market stock repurchase program (in shares)			6,600,000
Payments for shares repurchased under the current open-market stock repurchase program			$ 360,998
Quarterly dividend paid, per share (in dollars per share)	$ 0.015
Dividend paid	2,608	2,602	5,241	5,197
Dividends declared	$ 2,515	$ 2,603	$ 5,156	$ 5,204