STOCK-BASED COMPENSATION- Activity of stock incentive plans for options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options Shares Outstanding
Forfeited	(6,411)	(85,422)	(10,244)
Stock Incentive Plan | Stock Options
Options Shares Outstanding
Outstanding, beginning of period	1,643,255	922,026	746,004
Granted	15,500	949,500	170,500
Options assumed in acquisition			91,701
Exercise of stock options	(70,556)	(209,371)	(84,723)
Forfeited	(6,500)	(18,900)	(1,456)
Outstanding, ending of period	1,581,699	1,643,255	922,026
Exercisable	599,011
Weighted-Average Exercise Price
Outstanding	$ 39.82	$ 24.39	$ 21.56
Granted	52.76	49.93	36.86
Options assumed in acquisition			21.03
Exercise of stock options	21.52	18.15	20.98
Forfeited	39.43	35.36	21.71
Outstanding	40.77	$ 39.82	$ 24.39
Exercisable Shares	$ 32.77
Outstanding Shares, Weighted Average Remaining Life (in years)	7 years 4 months 17 days	8 years 1 month 6 days	5 years 4 months 13 days
Exercisable Shares, Weighted Average Remaining Life (in years)	6 years 3 months 14 days
Outstanding Shares, Aggregate Intrinsic Value	$ 13,825	$ 24,525	$ 21,483
Exercisable Shares, Aggregate Intrinsic Value	$ 9,798