NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cumulative Effect of ASU 2014-09 (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 5,150		$ 5,150			$ 2,606
Other long-term assets	678		678
Liabilities and Stockholders' Equity
Retained earnings	41,660		41,660			5,555
Income Statement
Provision (benefit) for income taxes	1,864	$ (55)	13,387	$ 269
Net Income	7,039	$ (2,830)	36,257	$ 13,120
Liabilities and Stockholders' Equity
Accrued income taxes	5,054		5,054			13
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Accounts receivable	0		0
Other long-term assets	0		0
Liabilities and Stockholders' Equity
Retained earnings	36,560		36,560
Liabilities and Stockholders' Equity
Accrued income taxes	4,326		4,326
Adjustments due to ASU 2014-09
Assets
Accounts receivable	(5,150)		(5,150)
Other long-term assets	(678)		(678)
Liabilities and Stockholders' Equity
Retained earnings	5,100		5,100
Liabilities and Stockholders' Equity
Accrued income taxes	728		728
Accounting Standards Update 2014-09
Assets
Accounts receivable					$ 5,156
Liabilities and Stockholders' Equity
Retained earnings					8,105
Income Statement
Revenues	17,300		82,300
Provision (benefit) for income taxes	1,864		13,387
Net Income	15,436		68,913
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Assets
Accounts receivable						2,606
Liabilities and Stockholders' Equity
Retained earnings						$ 5,555
Income Statement
Revenues	14,700		79,700
Provision (benefit) for income taxes	1,136		12,659
Net Income	13,564		67,041
Accounting Standards Update 2014-09 | Adjustments due to ASU 2014-09
Assets
Accounts receivable					2,550
Liabilities and Stockholders' Equity
Retained earnings					$ 2,550
Income Statement
Revenues	2,600		2,600
Provision (benefit) for income taxes	728		728
Net Income	$ 1,872		$ 1,872