Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 28, 2011	Feb. 28, 2009
Stockholders Equity Note [Line Items]
Common stock authorized to be repurchased, number of shares								20,000,000	20,000,000
Common stock repurchased, value					$ 214,195	$ 160,669	$ 35,725
Common stock dividends, paid per share	$ 0.07	$ 0.06	$ 0.06	$ 0.06
Common stock dividends, total cash paid					42,450	38,037
Common Stock and Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Common stock repurchased, shares					10,466,000	6,135,000	1,306,000
Common stock repurchased, value					214,195	160,669	35,725
Retained Earnings
Stockholders Equity Note [Line Items]
Common stock dividends, total cash paid					$ 42,450	$ 38,037