INCOME TAXES - Principal differences between federal statutory tax rate and income tax expense (Details 2)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	35.00%	35.00%
State taxes, net of federal tax benefit	(0.80%)	1.00%	3.80%
Excess of (decreases in) foreign tax over US tax on foreign income	2.90%	2.90%	(0.50%)
Remeasurement of deferred taxes under TCJA	0.00%	(7.70%)	0.00%
Deemed repatriation tax	(1.10%)	3.60%	0.00%
Domestic tax deductions and credits	(0.40%)	(3.10%)	(2.70%)
Foreign Derived Intangible Income deduction	(1.30%)	0.00%	0.00%
Release of unrecognized tax benefit	0.00%	(5.80%)	0.00%
Other	(1.30%)	(1.80%)	0.20%
Effective tax rate	19.00%	24.10%	35.80%