REVENUE RECOGNITION - Narrative (Details) $ in Thousands				12 Months Ended
	Sep. 29, 2020 USD ($)	Oct. 11, 2019 USD ($)	Sep. 30, 2019 USD ($) specific_radio_frequency	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Written termination period			30 days
Contracted exclusivity period				2 years
Revenue from collaboration agreement	$ 2,500
Deferred revenue				$ 1,783	$ 1,731	$ 271
Deferred revenue				62	0
Long-term Contract with Customer
Disaggregation of Revenue [Line Items]
Deferred revenue				62
Proprietary Circuit Designs using XBAR Technology | Murata Manufacturing Co., Ltd.
Disaggregation of Revenue [Line Items]
Number of licensed radio frequencies or bands | specific_radio_frequency			4
Prepaid royalties			$ 9,000
Contracted exclusivity period			30 months
Revenue from collaboration agreement				$ 2,700	$ 400
Proprietary Circuit Designs using XBAR Technology | Accounts Receivable | Murata Manufacturing Co., Ltd.
Disaggregation of Revenue [Line Items]
Revenue from collaboration agreement		$ 2,000