FEDERAL AND STATE CURRENT AND DEFERRED INCOME TAX - Difference Between Income Taxes at the Federal Statutory Rate and Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income tax (provision) benefit at statutory rate	$ (3,620)	$ 9,201	$ 13,083
Change in valuation allowance	36,055	(7,664)	(16,026)
Impact of U.S. tax reform	(35,570)
State taxes, net of federal benefit	319	225	280
Nondeductible compensation			(530)
Equity in loss of unconsolidated affiliate			2,766
Research and development credit			2,248
Other	(266)	(627)	1,140
Total income tax (provision) benefit	$ (3,082)	$ 1,135	$ 2,961