Share-Based Arrangements (Restricted Stock Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Nonqualified Stock Options and Restricted Stock [Member]
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]
Tax benefit from compensation expense	$ 2.2	$ 1.9	$ 1.7
Compensation cost not yet recognized	$ 7.4
Compensation cost recognized, period	3 years
Employee Stock Options and ESPP Stock [Member]
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]
Windfall tax benefit realized	$ 0.3	$ 0.8	0.5
Restricted Stock [Member]
Restricted Stock, Outstanding [Roll Forward]
Outstanding at beginning of period (in shares)	196,553
Granted (in shares)	80,494
Vested (in shares)	(91,640)
Forfeited or expired (in shares)	(1,864)
Outstanding at end of period (in shares)	183,543	196,553
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]
Outstanding at beginning of period (in dollars per share)	$ 36.29
Granted (in dollars per share)	39.83
Vested (in dollars per share)	36.37
Forfeited or expired (in dollars per share)	35.87
Outstanding at end of period (in dollars per share)	$ 37.80	$ 36.29
Total fair value of restricted stock awards vested	$ 3.8	$ 4.5	$ 4.6