Common Stock Plans (Stock Options) (Details) - Stock Incentive Plan - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Remaining reserved for issuance	2,294,740
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years
Share-based compensation, expiration period	10 years
Shares
Outstanding, Beginning of Period, Shares	757,071	1,191,044	1,648,475
Granted, Shares		110,307	137,762
Exercised, Shares	(23,680)	(544,280)	(590,119)
Forfeited, Shares			(5,074)
Outstanding, End of Period, Shares	733,391	757,071	1,191,044
Exercisable, Shares	622,156	454,938	713,445
Weighted Average Exercise Price
Outstanding, Beginning of Period, Weighted Average Exercise Price (in dollars per share)	$ 54.88	$ 51.06	$ 47.58
Granted, Weighted Average Exercise Price (in dollars per share)		72.55	49.22
Exercised, Weighted Average Exercise Price (in dollars per share)	41.42	50.09	40.92
Forfeited, Weighted Average Exercise Price (in dollars per share)			51.85
Outstanding, End of Period, Weighted Average Exercise Price (in dollars per share)	55.32	54.88	51.06
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 53.80	$ 51.88	$ 49.80