Shareholders' Equity (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2011
Stockholders Equity Note [Line Items]
Common stock authorized to be repurchased, number of shares						25,000,000
Common stock repurchased, value			$ 123,193,000	$ 139,238,000.000	$ 162,078,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	10,831,000		10,831,000
Common stock dividends, paid per share	$ 0.11	$ 0.10	$ 0.11	$ 0.10	$ 0.09
Common stock dividends, total cash paid			$ 61,399,000	$ 56,513,000	$ 51,404,000
Payments of Ordinary Dividends, Common Stock			$ 61,399,000	$ 56,513,000	$ 51,404,000
Common Stock and Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Common stock repurchased, shares			4,169,000	4,243,000	5,988,000
Common stock repurchased, value			$ 44,387,000	$ 122,851,000	$ 162,078,000
Retained Earnings
Stockholders Equity Note [Line Items]
Common stock repurchased, value			78,806,000	16,387,000
Common stock dividends, total cash paid			$ 61,399,000	$ 56,513,000	$ 51,404,000