Stock Based Compensation (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) years $ / shares shares	Dec. 31, 2014 USD ($) $ / shares	Dec. 31, 2013 USD ($) $ / shares
Number of shares authorized for stock based employee and non-employee compensation plans | shares	13.8
Employee [Member]
RSUs, vesting period (in years)	5
Director [Member]
RSUs, annual vesting percentage	100.00%
RSUs, vesting period (in years)	1
RSUs, contractual lives (in years)	1
Restricted Stock Units (RSUs) [Member]
Compensation expense recognized | $	$ 11.7	$ 12.3	$ 13.3
Total unrecognized compensation expense | $	$ 10.9
Total unrecognized compensation expense, weighted average recognition period	2 years 1 month
Restricted Stock Units (RSUs) [Member]
RSUs | $ / shares	$ 17.26	$ 15.03	$ 13.71
2015 Award Date [Member] | Employee [Member]
RSUs, vesting period (in years)	3