COMMON STOCK PLANS - Performance Share Awards (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Price
Share-based compensation expense	$ 15,402	$ 19,641	$ 12,910
Performance share awards
Weighted Average Price
Share-based compensation expense	7,400	6,200	6,700
Tax benefit related to stock-based compensation	1,400	$ 1,200	$ 2,400
Unrecognized compensation cost	$ 7,200
Weighted average requisite service period	1 year 1 month 13 days
Performance share awards | Stock Incentive Plan
Shares
Nonvested, Beginning of Period (in shares)	336,442	256,083	212,968
Forfeited (in shares)	(17,075)	(12,481)
Vested and paid (in shares)	(59,530)	(74,176)	(77,257)
Nonvested, End of Period (in shares)	400,037	336,442	256,083
Weighted Average Price
Nonvested, Beginning of Period, Weighted Average Price (in dollars per share)	$ 57.03	$ 80.43	$ 71.53
Forfeited, Weighted Average Price (in dollars per share)	48.55	72.30
Vested and paid, Weighted Average Price (in dollars per share)	93.52	63.88	61.36
Nonvested, End of Period, Weighted Average Price (in dollars per share)	$ 55.65	$ 57.03	$ 80.43
Performance share awards | Stock Incentive Plan | Two year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	2 years
Shares
Granted (in shares)	3,116
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)	$ 96.54
Performance share awards | Stock Incentive Plan | Three year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years	3 years	3 years
Shares
Granted (in shares)	137,084	167,016	120,372
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)	$ 66.89	$ 25.34	$ 83.94