Shareholders' Equity-Common Stock Rollforward (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Preferred Stock, Shares Authorized	2,000,000
Stock Repurchase Program, Authorized Amount	$ 1,600,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	1,136,543
Stock Repurchase Program, Remaining Authorized Repurchase Amount	463,457
Shares Approved December 2016 Member [Member]
Stock Repurchase Program, Authorized Amount	400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	400,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	0
Shares Approved December 2018 Member [Member]
Stock Repurchase Program, Authorized Amount	600,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	600,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	0
Shares Approved July 2020 Member [Member]
Stock Repurchase Program, Authorized Amount	600,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	136,543
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 463,457
Common Stock Issued [Member]
Common stock outstanding, Beginning balance	125,424	125,424	125,424
Shares issued for stock-based compensation awards	0	0	0
Repurchases of common stock	0	0	0
Common stock outstanding, Ending balance	125,424	125,424	125,424
Treasury Stock
Common stock outstanding, Beginning balance	44,804	40,233	37,733
Shares issued for stock-based compensation awards	764	886	709
Repurchases of common stock	(6,541)	(5,457)	(3,209)
Common stock outstanding, Ending balance	50,581	44,804	40,233
Common Stock at Par Value
Common stock outstanding, Beginning balance	80,620	85,191	87,691
Shares issued for stock-based compensation awards	764	886	709
Repurchases of common stock	(6,541)	(5,457)	(3,209)
Common stock outstanding, Ending balance	74,843	80,620	85,191