Nature Of Business And Summary Of Significant Accounting Policies (Narrative) (Details)		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($) segment note	Dec. 31, 2016 USD ($) note	Dec. 31, 2015 USD ($)	Jan. 01, 2017 USD ($)	Dec. 31, 2014 USD ($)
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Demonstration equipment, carrying value		$ 473,854,000	$ 391,086,000	$ 298,091,000
Bank acceptance drafts		$ 46,123,000	$ 23,975,000
Weighted average maturity period for bank acceptance drafts (less than)		90 days	90 days
Accrued warranty reported in accrued expenses and other liabilities		$ 25,059,000	$ 15,711,000
Accrued warranty reported in other long-term liabilities		22,458,000	18,267,000
Fair value		633,110,000	387,536,000
Available-for-sale securities, gross unrealized loss			432,000
Held-to-maturity securities, unrealized loss		96,000	163,000
Available-for-sale securities, cost basis		$ 1,012,000	$ 1,450,000
Number of outstanding long-term notes | note		2	2
Fair value, outstanding long-term notes		$ 49,884,000	$ 41,351,000
Number of operating segments | segment		1
Deferred tax assets		$ 26,976,000	42,442,000
Increase to retained earnings, less the tax impact		1,443,867,000	1,094,108,000
Retained Earnings
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle in period of adoption, increase (decrease)			2,145,000	0		$ 0
Accounting Standards Update 2016-09, Excess Tax Benefit Component
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred 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]
Cumulative effect of new accounting principle in period of adoption, increase (decrease)					3,464,000
Accounting Standards Update 2016-09, Forfeiture Rate Component
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred 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]
Cumulative effect of new accounting principle in period of adoption, increase (decrease)					(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]
Cumulative effect of new accounting principle in period of adoption, increase (decrease)		2,078,000	0	0	$ 2,078,000
Short-term investments
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value		206,161,000	206,616,000
Long-term notes
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value, outstanding long-term notes		48,982,000	41,351,000
Book value, outstanding long-term notes		$ 48,982,000	40,823,000
Minimum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Period for installation completion		30 days
Standard product warranty coverage period		1 year
Minimum | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Subsequent Event
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Decrease to deferred revenue	$ 600,000
Increase to retained earnings, less the tax impact	600,000
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
Maximum | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Subsequent Event
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Decrease to deferred revenue	900,000
Increase to retained earnings, less the tax impact	$ 900,000
Demonstration Equipment
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Demonstration equipment, economic useful life		3 years
Demonstration equipment, carrying value		$ 6,277,000	6,017,000
Demonstration equipment, amortization expense		$ 3,769,000	2,959,000	2,345,000
Intangible Assets | Minimum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Economic useful lives of intangible assets		5 years
Intangible Assets | Maximum
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Economic useful lives of intangible assets		13 years
Property, Plant and Equipment
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, impairment loss		$ 162,000	2,857,000	$ 0
Available-for-sale Securities
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value		$ 0	$ 41,591,000