Stock Award Plans, Employee Plan Stock Option Activity (Details) - Employee Stock Award Plan [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Award Plan Information [Abstract]
Shares available for future grants (in shares)	1,805,296
Stock Options [Member]
Stock Award Plan Information [Abstract]
Term of grant	7 years
Vesting period	3 years
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start (in shares)	601,121	430,432	322,956
Granted (in shares)	123,141	186,706	114,894
Exercised (in shares)	(36,616)
Canceled or expired (in shares)	(32,991)	(16,017)	(7,418)
Outstanding at Period End (in shares)	654,655	601,121	430,432
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start (in dollars per share)	$ 65.33	$ 71.01	$ 69.95
Granted (in dollars per share)	68.46	53.50	74.99
Exercised (in dollars per share)	47.95
Canceled or expired (in dollars per share)	74.07	80.17	86.28
Outstanding at Period End (in dollars per share)	$ 66.45	$ 65.33	$ 71.01
Stock options exercisable (in shares)	380,608	321,942	239,518
Stock Appreciation Rights [Member]
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period End (in shares)	0