Stock-Based Compensation and Other Employee Benefit Plans (Schedule of Employee Stock Purchase Plans) (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Common Stock [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Common shares issued (in shares)	55,138	49,502
Employee Stock Purchase Plans [Member]
Stock-Based Compensation and Other Employee Benefit Plans [Line Items]
Cash proceeds (in dollars)	$ 2.2	$ 1.6
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)	$ 39.99	$ 33.30
Weighted average per share grant date fair value (in dollars per share)	$ 9.74	$ 8.67