Stockholders' Equity (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	May 24, 2018	Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]
Treasury stock shares	1,100,000		1,200,000
Treasury stock, Cost basis	$ 24.1		$ 25.5
Restricted Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares nonvested	1,500,000		1,500,000
2018 Stock Buyback Program [Member]
Equity, Class of Treasury Stock [Line Items]
Shares authorized for repurchase		5.00%
Number of shares authorized for repurchase		4,300,000
Shares repurchased	0