Stockholders' Equity (Stock Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	Jan. 31, 2018
Stockholders' Equity Note [Abstract]
Repurchase and retirement of common stock, value	$ 40,000,000	$ 40,000,000
Share repurchase program, amount approved			$ 200,000,000
Remaining amount available for share repurchases under stock repurchase program	$ 160,000,000	$ 160,000,000
Repurchase and retirement of common stock (in shares)	1.0
Average cost per share repurchased (in dollars per share)	$ 38.87

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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Balance Type:	debit
Period Type:	duration