INCOME TAXES - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income taxes computed at federal statutory rate		$ 10,228	$ 5,912	$ 3,386
State income taxes, net of federal benefit		1,880	152	166
Foreign imputed interest		160	255	140
Meals and entertainment		346	422	361
Gain on sale of Vertex		0	0	(1,971)
Domestic production activity deduction		0	(98)	0
Research and development tax credit		(480)	(641)	(886)
Foreign tax credit		(346)	0	(383)
Valuation allowance		0	(791)	0
Tax reform deferred tax remeasurement		81	(1,294)	0
Canadian acquisition deferred tax liability true up	$ (2,200)	0	(2,180)	0
Foreign rate difference		150	(297)	112
Other		1,166	(1,077)	1,598
Total provision for income tax		$ 13,185	$ 363	$ 2,523