Stock Compensation Plans - Option Groups Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	6,597,098	7,173,048
Options exercisable (in shares)	4,913,448
Options remaining contractual term	5 years 3 months 18 days
Weighted average exercise price for options outstanding (in dollars per share)	$ 19.91	$ 18.21
Weighted average exercise price for options exercisable (in dollars per share)	$ 16.01
Remaining weighted average contractual term for options exercisable	4 years 3 months 18 days
Grant Date February 27 2017
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	685,669
Options exercisable (in shares)	0
Options exercise price (in dollars per share)	$ 35.26
Options remaining contractual term	9 years 2 months 12 days
Grant Date February 22 2016
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	669,719
Options exercisable (in shares)	180,041
Options exercise price (in dollars per share)	$ 29.90
Options remaining contractual term	8 years 2 months 12 days
Grant Date February 23 2015
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	607,101
Options exercisable (in shares)	315,735
Options exercise price (in dollars per share)	$ 27.16
Options remaining contractual term	7 years 2 months 12 days
Grant Date February 24 2014
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	415,862
Options exercisable (in shares)	312,824
Options exercise price (in dollars per share)	$ 26.44
Options remaining contractual term	6 years 2 months 12 days
Grant Date February 28 2013
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	1,064,424
Options exercisable (in shares)	1,064,424
Options exercise price (in dollars per share)	$ 12.98
Options remaining contractual term	5 years 2 months 12 days
Grant Date February 27 2012
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	838,311
Options exercisable (in shares)	838,311
Options exercise price (in dollars per share)	$ 12.94
Options remaining contractual term	4 years 2 months 12 days
Grant Date February 22 2011
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	609,805
Options exercisable (in shares)	609,805
Options exercise price (in dollars per share)	$ 13.91
Options remaining contractual term	3 years 1 month 12 days
Grant Date February 23 2010
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	435,696
Options exercisable (in shares)	435,696
Options exercise price (in dollars per share)	$ 12.74
Options remaining contractual term	2 years 1 month 12 days
Grant Date February 26 2009
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	330,916
Options exercisable (in shares)	330,916
Options exercise price (in dollars per share)	$ 4.81
Options remaining contractual term	1 year 2 months 12 days
Grant Date February 21 2008
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	149,241
Options exercisable (in shares)	149,241
Options exercise price (in dollars per share)	$ 26.74
Options remaining contractual term	1 month 12 days
All Other Grant Dates
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	790,354
Options exercisable (in shares)	676,455
Options remaining contractual term	5 years
Other options exercise price range, lower range limit (in dollars per share)	$ 6.22
Other options exercise price range, upper range limit (in dollars per share)	36.25
Weighted average exercise price for options outstanding (in dollars per share)	19.50
Weighted average exercise price for options exercisable (in dollars per share)	$ 17.97
Remaining weighted average contractual term for options exercisable	4 years 6 months