Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017
Income Tax [Line Items]
Tax Cuts and Jobs Act of 2017, Provisional income tax expense (benefit)	$ 10,400
Provision for (benefit from) income taxes		$ 10,647	$ (1,836)	$ (1,062)
Valuation allowance		10,094	9,100
Increase in valuation allowance		1,000	3,300
Unrecognized tax benefits that would impact effective tax rate	$ 2,800	4,200	$ 3,500	$ 2,800
State
Income Tax [Line Items]
Operating loss carryforwards		2,100
State | Research and Development Credits [Member]
Income Tax [Line Items]
Tax credit carryforward		13,200
Domestic Tax Authority [Member]
Income Tax [Line Items]
Operating loss carryforwards		5,000
Domestic Tax Authority [Member] | Research and Development Credits [Member]
Income Tax [Line Items]
Tax credit carryforward		14,600
Foreign Tax Authority
Income Tax [Line Items]
Tax credit carryforward		$ 2,600
Accounting Standards Update 2016-09
Income Tax [Line Items]
Cumulative effect of a change in accounting principle related to stock-based compensation					$ 7,745
Retained earnings | Accounting Standards Update 2016-09
Income Tax [Line Items]
Cumulative effect of a change in accounting principle related to stock-based compensation					$ 7,745