UNAUDITED QUARTERLY OPERATING RESULTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Product revenues, net	$ 27,362	$ 78,843	$ 82,942	$ 87,721	$ 76,271	$ 79,176	$ 78,058	$ 76,511	$ 276,868	$ 310,016	$ 296,701
Cost of product revenues (excluding intangible asset amortization)	11,900	15,934	15,908	15,328	15,184	14,188	12,899	27,229	59,070	69,500	178,908
Intangible asset amortization	16,795	16,796	16,795	16,795	16,795	16,795	16,795	10,295	67,181	60,680	14,752
Total cost of products revenues	28,695	32,730	32,703	32,123	31,979	30,983	29,694	37,524	126,251	130,180	193,660
Gross profit	(1,333)	46,113	50,239	55,598	44,292	48,193	48,364	38,987	150,617	179,836	103,041
Research and development	1,609	1,450	3,462	2,930	2,472	2,141	2,493	2,666	9,451	9,772	10,340
Selling, general and administrative	26,602	30,514	30,368	31,476	26,824	26,426	29,322	31,260	118,960	113,832	116,449
Restructuring	4,578								4,578
Total operating expenses	32,789	31,964	33,830	34,406	29,296	28,567	31,815	33,926	132,989	123,604	126,789
Income (loss) from operations	(34,122)	14,149	16,409	21,192	14,996	19,626	16,549	5,061	17,628	56,232	(23,748)
Interest expense	(4,757)	(5,115)	(5,421)	(5,721)	(7,737)	(8,063)	(8,259)	(4,823)	(21,014)	(28,882)	(909)
Interest income	3	3	3	3	3	3	14	212	12	232	1,935
(Loss) income before income taxes	(38,876)	9,037	10,991	15,474	7,262	11,566	8,304	450	(3,374)	27,582	(22,722)
(Benefit from) provision for income taxes	(13,842)	991	(61,852)	(188)	304	280		246	(74,891)	830	0
Net income (loss)	$ (25,034)	$ 8,046	$ 72,843	$ 15,662	$ 6,958	$ 11,286	$ 8,058	$ 450	$ 71,517	$ 26,752	$ (22,722)
Earnings (loss) per share - basic (in dollars per share)	$ (0.73)	$ 0.23	$ 2.06	$ 0.45	$ 0.20	$ 0.33	$ 0.23	$ 0.01	$ 2.05	$ 0.78	$ (0.68)
Weighted-average shares - basic (in shares)	34,123,309	35,373,909	35,302,608	34,951,740	34,592,277	34,540,126	34,395,266	34,100,688	34,936,817	34,407,959	33,453,844
Earnings (loss) per share - diluted (in dollars per share)	$ (0.73)	$ 0.22	$ 1.79	$ 0.41	$ 0.20	$ 0.32	$ 0.23	$ 0.01	$ 1.86	$ 0.76	$ (0.68)
Weighted-average shares - diluted (in shares)	34,123,309	36,261,174	41,286,853	41,160,092	35,417,623	35,069,188	35,091,906	35,069,693	41,045,805	35,151,353	33,453,844
Selling, general and administrative expenses
Litigation settlements	$ 2,935
Xtampza ER
Product revenues, net									$ 103,708	$ 127,984	$ 105,012
Nucynta Products
Product revenues, net									$ 173,160	$ 182,032	$ 191,689
Estimates of Product Returned [Member] | Adjustment
Product revenues, net	(38,329)
Estimates of Product Returned [Member] | Adjustment | Xtampza ER
Product revenues, net	(13,787)
Estimates of Product Returned [Member] | Adjustment | Nucynta Products
Product revenues, net	$ (24,542)