Restatement of Consolidated Financial Statements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended	9 Months Ended			12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Error corrections and prior period adjustments restatement
Revenue	$ 61,913	$ 56,915	$ 61,717	$ 65,777	$ 61,735	$ 59,187	$ 58,297	$ 48,384	$ 127,494	$ 184,409	$ 165,868		$ 246,322	$ 227,603	$ 231,201
Proceeds from sale of assets held for sale				0					0	0	0	$ 4,648	0	0	4,648
Royalties
Error corrections and prior period adjustments restatement
Revenue		$ 16,602	18,744	21,482		21,236			40,226	56,828	73,139		84,560	94,361	130,452
Adjustments
Error corrections and prior period adjustments restatement
Revenue			1,787	1,788		1,788			3,575	3,575	1,788		3,575	3,576
Proceeds from sale of assets held for sale												$ 894			$ 894
Adjustments | Sunnyvale Facility, Second Amended
Error corrections and prior period adjustments restatement
Asset retirement obligation					$ 1,000									1,000
Adjustments | Royalties
Error corrections and prior period adjustments restatement
Revenue			$ 1,787	$ 1,788		$ 1,788			$ 3,575	$ 3,575	$ 1,788		$ 3,575	$ 3,576