Asset sale (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement receivable (Note 5)			$ 12,263	$ 11,999
Transition services agreement payables (see Note 6)			11,776	11,769
Assets held for sale			3,074	$ 2,971
Gain within operating income		$ 2,200
Other current liabilities | Indemnification agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset sale related contingent liabilities (see Note 6)			$ 6,900
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale					$ 13,900
Reclassification from assets held-for-sale	$ 3,400
Assets sold	12,800
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Inventories
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, other					13,100
Assets sold	12,100
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Property, plant and equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, other					$ 800
Assets sold	700
Low Speed Transceiver Products | APAT OE | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received pursuant to asset purchase agreement	25,000
Proceeds from post-closing transaction services fees under transition services agreement	1,400
Disposal group consideration adjustment	21,600
Consideration adjustment for potential indemnification claims	$ 10,000