Nature Of Business And Summary Of Significant Accounting Policies (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) segment numberOfCustomers $ / shares customer shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Feb. 27, 2019 USD ($)	Jan. 01, 2018 USD ($)	Jan. 01, 2017 USD ($)
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Bank acceptances drafts		$ 27,335,000	$ 46,123,000
Bank acceptances, weighted-average maturity period		90 days	90 days
Long-lived assets		$ 553,732,000	$ 473,854,000
Common stock, shares authorized (in shares) | shares		175,000,000	175,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares) | shares		5,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.0001
Number of customers | numberOfCustomers		1
Number of largest customers | customer		5
Net sales by major customers, percentage		26.00%	28.00%	22.00%
Number of operating segments | segment		1
Deferred income tax assets		$ 19,165,000	$ 26,976,000			$ 28,150,000
Recently adopted accounting standards						616,000	$ 4,223,000
Retained Earnings
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Recently adopted accounting standards						$ 606,000	2,145,000
Additional Paid In Capital
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Recently adopted accounting standards							2,078,000
ASU 2018-02
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings	$ 10,000
Accounting Standards Update 2016-09, Excess Tax Benefit Component
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred income tax assets							3,464,000
Accounting Standards Update 2016-09, Excess Tax Benefit Component | Retained Earnings
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Recently adopted accounting standards							3,464,000
Accounting Standards Update 2016-09, Forfeiture Rate Component
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred income tax assets							759,000
Accounting Standards Update 2016-09, Forfeiture Rate Component | Retained Earnings
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Recently adopted accounting standards							(1,319,000)
Accounting Standards Update 2016-09, Forfeiture Rate Component | Additional Paid In Capital
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Recently adopted accounting standards							$ 2,078,000
Minimum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Period for installation completion		1 year
Standard product warranty coverage period		1 year
Maximum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Period for installation completion		90 days
Standard product warranty coverage period		3 years
Demonstration Equipment
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment useful life		3 years
Long-lived assets		$ 7,037,000	6,277,000
Amortization		$ 3,870,000	3,769,000	$ 2,959,000
Intangible Assets | Minimum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Intangible asset, useful life		1 year
Intangible Assets | Maximum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Intangible asset, useful life		13 years
Property, Plant and Equipment
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Impairment losses		$ 0	$ 162,000	$ 2,857,000
Sales
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Percentage of net sales		12.00%	13.00%	9.00%
Subsequent Event | Accounting Standards Update 2016-02
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Lease liability					$ 25,000,000