COMMON STOCK PLANS - Stock Options (Details) - Stock Incentive Plan - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Remaining reserved for issuance (in shares)	1,444,057
Stock options
Shares
Outstanding, Beginning of Period (in shares)	710,901	733,391	757,071
Exercised (in shares)	(6,052)	(22,490)	(23,680)
Expired (in shares)	(27,284)
Outstanding, End of Period (in shares)	677,565	710,901	733,391
Exercisable (in shares)	677,565	676,271	622,156
Weighted Average Exercise Price
Outstanding, Beginning of Period, Weighted Average Exercise Price (in dollars per share)	$ 55.66	$ 55.32	$ 54.88
Exercised, Weighted Average Exercise Price (in dollars per share)	48.36	44.60	41.42
Expired, Weighted Average Exercise Price (in dollars per share)	58.40
Outstanding, End of Period, Weighted Average Exercise Price (in dollars per share)	55.61	55.66	55.32
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 55.61	$ 54.79	$ 53.80