Stockholders’ Equity and Earnings Per Share (Earnings Per Share) (Details) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefits due to ASU 2016-09 \| $	$ 4.8
Accounting Standards Update 2016-09
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefits due to ASU 2016-09 (in dollars per share) \| $ / shares	$ 0.03

Amount of the effect of a change in accounting principle on basic earnings per share.

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