Stock-Based Compensation and Other Employee Benefit Plans (Schedule of Employee Stock Purchase Plans) (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Common Stock [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Common shares issued (in shares)	79,459	68,789
Employee Stock Purchase Plans [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Cash proceeds (in dollars)	$ 3.1	$ 2.4
Employee Stock Purchase Plans [Member] \| Common Stock [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Weighted average price per share (in dollars per share)	$ 39.36	$ 34.72
Weighted average per share grant date fair value (in dollars per share)	$ 9.62	$ 9.00

Amount of cash inflow from issuance of shares under share-based compensation arrangement, excluding stock option exercises.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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