Cash and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 140,365	$ 129,959
Gross Unrealized Gains	3	19
Gross Unrealized Losses	(11)	(17)
Estimated Fair Market Value	140,357	129,961
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,001	11,412
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(7)
Estimated Fair Market Value	1,996	11,405
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	17,907	22,402
Gross Unrealized Gains	3	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	17,910	22,402
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	45,701	14,194
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(6)
Estimated Fair Market Value	45,697	14,188
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,916	5,466
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(3)
Estimated Fair Market Value	6,914	5,463
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	38,235	43,604
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	38,235	43,604
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	812	959
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	812	959
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,298	23,000
Gross Unrealized Gains	0	19
Gross Unrealized Losses	0	0
Estimated Fair Market Value	23,298	23,019
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	501	5,667
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	501	5,667
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,994	2,499
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	$ 4,994	2,499
Municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		756
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Estimated Fair Market Value		$ 755

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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