Revenue - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 87,493	$ 72,523	$ 268,201	$ 216,763
Increase/(decrease) in disaggregated revenue	$ 14,970		$ 51,438
Percentage increase/(decrease) in disaggregated revenue	21.00%		24.00%
Variable patent royalty revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 7,377	4,683	$ 17,920	22,557
Increase/(decrease) in disaggregated revenue	$ 2,694		$ (4,637)
Percentage increase/(decrease) in disaggregated revenue	58.00%		(21.00%)
Fixed-fee royalty revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 77,338	63,736	$ 221,023	190,345
Increase/(decrease) in disaggregated revenue	$ 13,602		$ 30,678
Percentage increase/(decrease) in disaggregated revenue	21.00%		16.00%
Current patent royalties
Disaggregation of Revenue [Line Items]
Revenue	$ 84,715	68,419	$ 238,943	212,902
Increase/(decrease) in disaggregated revenue	$ 16,296		$ 26,041
Percentage increase/(decrease) in disaggregated revenue	24.00%		12.00%
Non-current patent royalties
Disaggregation of Revenue [Line Items]
Revenue	$ 507	(370)	$ 20,461	(4,908)
Increase/(decrease) in disaggregated revenue	$ 877		$ 25,369
Percentage increase/(decrease) in disaggregated revenue	237.00%		517.00%
Total patent royalties
Disaggregation of Revenue [Line Items]
Revenue	$ 85,222	68,049	$ 259,404	207,994
Increase/(decrease) in disaggregated revenue	$ 17,173		$ 51,410
Percentage increase/(decrease) in disaggregated revenue	25.00%		25.00%
Current technology solutions revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 2,271	3,724	$ 8,797	7,794
Increase/(decrease) in disaggregated revenue	$ (1,453)		$ 1,003
Percentage increase/(decrease) in disaggregated revenue	(39.00%)		13.00%
Patent sales
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 750	$ 0	$ 975
Increase/(decrease) in disaggregated revenue	$ (750)		$ (975)
Percentage increase/(decrease) in disaggregated revenue	(100.00%)		(100.00%)