Shareholders' Equity-Common Stock Rollforward (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 01, 2016
Preferred Stock, Shares Authorized	2,000,000
Stock Repurchase Program, Authorized Amount	$ 600,000			$ 400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	0			271,388
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 600,000			$ 128,612
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	37,733	36,511	34,501
Shares issued for stock-based compensation awards	(709)	(1,097)	(1,372)
Repurchases of common stock	3,209	2,319	3,382
Common stock outstanding, Ending balance	40,233	37,733	36,511
Common Stock at Par Value
Common stock outstanding, Beginning balance	87,691	88,913	90,923
Shares issued for stock-based compensation awards	709	1,097	1,372
Repurchases of common stock	(3,209)	(2,319)	(3,382)
Common stock outstanding, Ending balance	85,191	87,691	88,913