Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 18, 2016	Feb. 16, 2015	Nov. 13, 2014	Feb. 17, 2014	May. 23, 2013	May. 22, 2013	Feb. 19, 2013	Feb. 18, 2013
Common stock, shares authorized		305,000,000	305,000,000						305,000,000.0	120,000,000.0
Stock split, conversion ratio	3
Common Stock Dividends, Shares, Percentage	200.00%
Stock Issued During Period, Shares, Stock Splits	117,861,772
Common shares, par value (in dollars per share)	$ 1.25	$ 1.25	$ 1.25
Adjustments to Additional Paid in Capital, Stock Split	$ 147,300
Dividend Per Common Share Minimum						$ 0.16		$ 0.14			$ 0.12
Dividend Per Common Share Maximum						$ 0.18		$ 0.16			$ 0.14
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 160,700
Treasury stock, acquired		$ 303,651	$ 246,504	$ 458,310
Share repurchase program 2015
Stock Repurchase Program, Authorized Amount							$ 500,000					$ 750,000
Treasury stock, shares acquired		6,047,839
Treasury stock, acquired		$ 303,700
Share Repurchase Program 2014
Stock Repurchase Program, Remaining Authorized Repurchase Amount							$ 175,000
Treasury stock, shares acquired			3,420,656
Treasury stock, acquired			$ 246,500
Share Repurchase Program 2013
Treasury stock, shares acquired				8,142,723
Treasury stock, acquired				$ 458,300
Subsequent Event
Dividend Per Common Share Minimum					$ 0.18
Dividend Per Common Share Maximum					$ 0.19