Operations and summary of significant accounting policies - Narrative (Details)		12 Months Ended
	Jan. 15, 2020 USD ($) employee	Dec. 31, 2019 USD ($) ft² segment reporting_unit source shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Jan. 01, 2019 USD ($)	Dec. 31, 2016 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Gain on sale of assets		$ 26,842,000	$ 0	$ 0
Number of primary sources of revenue | source		2
Allowances for doubtful accounts		$ 3,543,000	3,490,000	2,892,000		$ 1,867,000
Allowances for sales returns		$ 2,600,000	2,300,000
Short-term investments-available-for sale, contractual maturity		60 months
Short-term investments denominated in Euro		$ 238,000,000	271,000,000
Net sale of short-term investments		34,000,000
Cumulative net adjustment for excess and obsolete inventories		$ 15,489,000	15,385,000	$ 16,447,000		$ 12,639,000
Number of operating segments | segment		1
Number of reporting units | reporting_unit		1
Goodwill impairment		$ 0	0
Cash, cash equivalents, and short-term investments		433,000,000
Cash and cash equivalents		$ 194,616,000	$ 259,386,000
Maximum maturity period for marketable securities		5 years
Maximum weighted average maturity period (in months)		24 months
Minimum percentage maturing in 90 days or less		10.00%
Maturity period		90 days
Percentage of sales to any individual customer to total revenue		3.00%	3.00%	3.00%
Largest trade account receivable from any individual customer		$ 4,600,000
Limited warranty on most hardware products (in number of years)		1 year
Advertising expense		$ 7,000,000	$ 8,000,000	$ 11,000,000
Anti-dilutive securities excluded from the computation of diluted EPS (in shares) | shares		94,206	11,352	32,400
Comprehensive income		$ 158,012,000	$ 154,635,000	$ 70,523,000
Operating lease liabilities		54,081,000			$ 52,000,000
Property, plant and equipment, net		243,717,000	$ 245,201,000
Operating lease right-of-use assets		$ 70,407,000			52,000,000
Leaseholds and Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, net					19,000,000
Minimum | Buildings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets		20 years
Minimum | Furniture And Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets		3 years
Minimum | Acquired Software Products
Summary Of Significant Accounting Policies [Line Items]
Useful life		3 years
Minimum | Patents
Summary Of Significant Accounting Policies [Line Items]
Useful life		10 years
Maximum | Buildings
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets		40 years
Maximum | Furniture And Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets		7 years
Maximum | Acquired Software Products
Summary Of Significant Accounting Policies [Line Items]
Useful life		6 years
Maximum | Patents
Summary Of Significant Accounting Policies [Line Items]
Useful life		17 years
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, net					226,595,000
Operating lease right-of-use assets					68,938,000
Accounting Standards Update 2016-02 | Leaseholds and Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets					$ 19,000,000
Hungarian Citibank
Summary Of Significant Accounting Policies [Line Items]
Short-term investments denominated in Euro		$ 5,000,000
Malaysian Citibank
Summary Of Significant Accounting Policies [Line Items]
Short-term investments denominated in Euro		5,000,000
Cash and cash equivalents		$ 13,000,000
Malaysian Citibank | Credit Concentration Risk | Cash and Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage		7.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Millennium Property
Summary Of Significant Accounting Policies [Line Items]
Gain on sale of assets		$ 26,800,000
Area of property | ft²		136,000
Disposal Group, Held-for-sale, Not Discontinued Operations | AWR Corp.
Summary Of Significant Accounting Policies [Line Items]
Liabilities		$ 21,148,000
Subsequent Event | Disposal Group, Held-for-sale, Not Discontinued Operations | AWR Corp.
Summary Of Significant Accounting Policies [Line Items]
Cash	$ 160,000,000
Realized Gain (Loss) on sale of properties	$ 123,000,000
Number of employees | employee	110