Stock Based Compensation (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) years $ / shares shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
Number of shares authorized for stock based employee and non-employee compensation plans | shares	10.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | $	$ 17.7	$ 18.3	$ 19.3
Employee [Member]
RSUs, vesting period (in years)	5
Director [Member]
RSUs, vesting period (in years)	1
RSUs, annual vesting percentage	100.00%
RSUs, contractual lives (in years)	1
Restricted Stock Units (RSUs) [Member]
Compensation expense recognized | $	$ 11.0	$ 11.9	$ 11.2
Total unrecognized compensation expense | $	$ 6.0
Total unrecognized compensation expense, weighted average recognition period	1 year 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares	$ 29.98	$ 25.38	$ 25.42
RSUs | $ / shares	$ 27.73	$ 23.36	$ 20.79
2015 Award Date [Member] | Employee [Member]
RSUs, vesting period (in years)	3