Stock Compensation Plans - Option Groups Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	5,580,452	6,597,098
Options exercisable (in shares)	4,717,476
Options remaining contractual term	4 years 6 months
Weighted average exercise price for options outstanding (in dollars per share)	$ 20.14	$ 19.91
Weighted average exercise price for options exercisable (in dollars per share)	$ 17.93
Remaining weighted average contractual term for options exercisable	4 years
Grant Date February 27 2017
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	615,265
Options exercisable (in shares)	187,801
Options exercise price (in dollars per share)	$ 35.26
Options remaining contractual term	8 years 2 months 12 days
Grant Date February 22 2016
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	598,622
Options exercisable (in shares)	324,268
Options exercise price (in dollars per share)	$ 29.90
Options remaining contractual term	7 years 2 months 12 days
Grant Date February 23 2015
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	544,078
Options exercisable (in shares)	420,286
Options exercise price (in dollars per share)	$ 27.16
Options remaining contractual term	6 years 2 months 12 days
Grant Date February 24 2014
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	391,667
Options exercisable (in shares)	391,667
Options exercise price (in dollars per share)	$ 26.44
Options remaining contractual term	5 years 2 months 12 days
Grant Date February 28 2013
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	963,158
Options exercisable (in shares)	963,158
Options exercise price (in dollars per share)	$ 12.98
Options remaining contractual term	4 years 2 months 12 days
Grant Date February 27 2012
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	748,001
Options exercisable (in shares)	748,001
Options exercise price (in dollars per share)	$ 12.94
Options remaining contractual term	3 years 2 months 12 days
Grant Date February 22 2011
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	545,267
Options exercisable (in shares)	545,267
Options exercise price (in dollars per share)	$ 13.91
Options remaining contractual term	2 years 1 month 6 days
Grant Date February 23 2010
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	377,324
Options exercisable (in shares)	377,324
Options exercise price (in dollars per share)	$ 12.74
Options remaining contractual term	1 year 1 month 6 days
Grant Date February 26 2009
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	159,212
Options exercisable (in shares)	159,212
Options exercise price (in dollars per share)	$ 4.81
Options remaining contractual term	2 months 12 days
All Other Grant Dates
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (in shares)	637,858
Options exercisable (in shares)	600,492
Options remaining contractual term	4 years 2 months 12 days
Other options exercise price range, lower range limit (in dollars per share)	$ 7.02
Other options exercise price range, upper range limit (in dollars per share)	32.72
Weighted average exercise price for options outstanding (in dollars per share)	19.31
Weighted average exercise price for options exercisable (in dollars per share)	$ 18.58
Remaining weighted average contractual term for options exercisable	3 years 10 months 24 days