Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 25, 2013	Feb. 28, 2011
Stockholders Equity Note [Line Items]
Common stock authorized to be repurchased, number of shares	15,000,000	15,000,000			25,000,000	25,000,000
Common stock repurchased, value		$ 139,238	$ 162,078	$ 214,195
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	14,769,000	14,769,000
Common stock dividends, paid per share	$ 0.10		$ 0.09	$ 0.07
Common stock dividends, total cash paid		56,513	51,404	42,450
Common Stock and Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Common stock repurchased, shares		4,243,000	5,988,000	10,466,000
Common stock repurchased, value		122,851	162,078	214,195
Retained Earnings
Stockholders Equity Note [Line Items]
Common stock repurchased, value		16,387
Common stock dividends, total cash paid		$ 56,513	$ 51,404	$ 42,450