STOCK-BASED PLANS (Summary of Restricted Stock Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted Average Grant Date Fair Value
Stock based compensation expense	$ 7,385	$ 6,707	$ 7,284
Restricted Stock
Restricted stock activity
Vesting period	5 years
Restricted stock outstanding at the beginning of the period (in shares)	289,112	242,556	172,690
Granted (in shares)	177,385	136,198		81,581
Vested (in shares)	(68,819)	(37,670)	(7,546)
Forfeited (in shares)	(43,482)	(51,972)	(4,169)
Restricted stock outstanding at the end of the period (in shares)	354,196	289,112	242,556	172,690
Weighted Average Grant Date Fair Value
Restricted stock outstanding at the beginning of the period (in dollars per share)	$ 88.88	$ 100.15	$ 121.81
Granted (in dollars per share)	85.81	67.80		$ 121.81
Vested (in dollars per share)	88.58	83.47	147.56
Forfeited (in dollars per share)	76.10	90.14	101.33
Restricted stock outstanding at the end of the period (in dollars per share)	$ 88.97	$ 88.88	$ 100.15	$ 121.81
Fair value of restricted stock vested	$ 8,900
Unamortized restricted stock expense	$ 20,300
Weighted-average period for recognition of unamortized restricted stock expense	4 years 2 months 12 days
Restricted Stock | General and Administrative Expense
Weighted Average Grant Date Fair Value
Stock based compensation expense	$ 5,700	$ 4,500	$ 4,700
Stock Options
Weighted Average Grant Date Fair Value
Stock based compensation expense	8,400	9,400	9,800
Share based compensation costs capitalized	$ 1,100	2,600	2,500
Weighted-average period for recognition of unamortized restricted stock expense	3 years
Stock Options | General and Administrative Expense
Weighted Average Grant Date Fair Value
Stock based compensation expense	$ 1,600	$ 2,900	$ 2,600