Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended
	Apr. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Jan. 31, 2011 Y
Shareholders' Equity
Number of shares authorized to be repurchased under the current open-market stock repurchase program					20,000,000
Repurchase of stock program, period (in years)					3
Statement
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)	$ 48,249	$ 81,885		$ 188,503
Quarter dividend paid, per share (in dollars per share)	$ 0.105
Dividends declared per common share (in dollars per share)		$ 0.105	$ 0.015	$ 0.015
Dividend paid (in dollars)		2,448		2,633
Cumulative dividends declared		17,049		2,642
Repurchase of common stock
Statement
Number of shares repurchased under the current open-market stock repurchase program	845,000	1,495,910
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)	$ 48,249	$ 81,885
Remaining number of shares authorized to be repurchased under the current open-market stock repurchase program	4,230,700