SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Recently adopted accounting standards (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 30, 2018
Recently adopted accounting standards [Abstract]
Operating lease right-of-use assets	$ 38,717	$ 39,000	$ 0
Present value of lease liabilities	$ 41,361	$ 41,000