Shareholders' Equity-Common Stock Rollforward (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock, Shares Authorized	2,000,000
Stock Repurchase Program, Authorized Amount	$ 1,000,000	$ 600,000		$ 400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	661,463	261,463		400,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 338,537	$ 338,537		$ 0
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	40,233	37,733	36,511
Shares issued for stock-based compensation awards	(886)	(709)	(1,097)
Repurchases of common stock	5,457	3,209	2,319
Common stock outstanding, Ending balance	44,804	40,233	37,733
Common Stock at Par Value
Common stock outstanding, Beginning balance	85,191	87,691	88,913
Shares issued for stock-based compensation awards	886	709	1,097
Repurchases of common stock	(5,457)	(3,209)	(2,319)
Common stock outstanding, Ending balance	80,620	85,191	87,691