REVENUE RECOGNITION - Impact of Adoption of ASC 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenues:
Royalty and license	$ 85,335	$ 9,006
Development, services, and other	81	218
Total revenues	85,416	9,224
Operating Expenses	15,311
Operating income (loss)	70,105	(12,852)
Interest and other income	231	139
Income (loss) before provision for income taxes	70,336	(12,713)
Provision for income taxes	(453)	(152)
Net income (loss)	$ 69,883	$ (12,865)
Basic net loss per share (in dollars per share)	$ 2.35	$ (0.44)
Diluted net loss per share (in dollars per share)	$ 2.29	$ (0.44)
Balance Sheets
Prepaid expenses and other current assets	$ 5,616		$ 5,732	$ 736
Other assets	4,808			344
Deferred revenue - current	(4,920)		(2,658)	(4,424)
Long-term deferred revenue	(33,665)		(10,730)	(22,303)
Accumulated deficit	83,398		153,281	171,616
Fixed fee license revenue
Revenues:
Royalty and license	75,756
Per-unit royalty revenue
Revenues:
Royalty and license	9,579
Calculated under revenue guidance in effect before Topic 606
Revenues:
Royalty and license	8,643	$ 9,006
Development, services, and other	81	218
Total revenues	8,724	9,224
Operating Expenses	15,311	22,076
Operating income (loss)	(6,587)	(12,852)
Interest and other income	231	139
Income (loss) before provision for income taxes	(6,356)	(12,713)
Provision for income taxes	(453)	(152)
Net income (loss)	$ (6,809)	$ (12,865)
Basic net loss per share (in dollars per share)	$ (0.23)	$ (0.44)
Diluted net loss per share (in dollars per share)	$ (0.22)	$ (0.44)
Balance Sheets
Prepaid expenses and other current assets	$ 769			736
Other assets	308			344
Deferred revenue - current	(14,441)			(4,424)
Long-term deferred revenue	(109,825)			(22,303)
Accumulated deficit	178,425			$ 171,616
Calculated under revenue guidance in effect before Topic 606 | Fixed fee license revenue
Revenues:
Royalty and license	3,415	$ 2,510
Calculated under revenue guidance in effect before Topic 606 | Per-unit royalty revenue
Revenues:
Royalty and license	5,228	$ 6,496
Accounting Standards Update 2014-09 | Difference between revenue guidance in effect before and after Topic 606
Revenues:
Royalty and license	(76,692)
Development, services, and other	0
Total revenues	(76,692)
Operating Expenses	0
Operating income (loss)	(76,692)
Interest and other income	0
Income (loss) before provision for income taxes	(76,692)
Provision for income taxes	0
Net income (loss)	$ (76,692)
Basic net loss per share (in dollars per share)	$ (2.58)
Diluted net loss per share (in dollars per share)	$ (2.51)
Balance Sheets
Prepaid expenses and other current assets	$ (4,847)		4,996
Other assets	(4,500)
Deferred revenue - current	(9,521)		1,766
Long-term deferred revenue	(76,160)		11,573
Accumulated deficit	95,027		(18,335)
Accounting Standards Update 2014-09 | Difference between revenue guidance in effect before and after Topic 606 | Fixed fee license revenue
Revenues:
Royalty and license	(72,341)
Balance Sheets
Deferred revenue - current			1,766
Long-term deferred revenue			11,573
Accumulated deficit			(13,339)
Accounting Standards Update 2014-09 | Difference between revenue guidance in effect before and after Topic 606 | Per-unit royalty revenue
Revenues:
Royalty and license	$ (4,351)
Balance Sheets
Prepaid expenses and other current assets			4,996
Accumulated deficit			$ (4,996)