Summary of Significant Accounting Policies - Summary of Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Market Value of Cash and Cash Equivalents and Available-for-Sale Investments (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	$ 100,551,000
Gross Unrealized Gains	9,000
Gross Unrealized Losses	(19,000)
Fair Value	100,541,000	$ 0
Cash
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	10,667,000
Fair Value	10,667,000
Cash Equivalents
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Fair Value		$ 0
Cash Equivalents | Money Market Funds
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	14,065,000
Fair Value	14,065,000
Cash Equivalents | U.S. Government Agency Securities
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	4,996,000
Gross Unrealized Gains	1,000
Fair Value	4,997,000
Cash Equivalents | Corporate Notes and Bonds
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	959,000
Fair Value	959,000
Cash Equivalents | Commercial Paper
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	2,948,000
Fair Value	2,948,000
Short-term Investments | U.S. Government Agency Securities
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	36,535,000
Gross Unrealized Gains	6,000
Gross Unrealized Losses	(10,000)
Fair Value	36,531,000
Short-term Investments | Corporate Notes and Bonds
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	19,259,000
Gross Unrealized Gains	2,000
Gross Unrealized Losses	(9,000)
Fair Value	19,252,000
Short-term Investments | Commercial Paper
Schedule Of Cash Cash Equivalents And Investments [Line Items]
Amortized Cost	11,122,000
Fair Value	$ 11,122,000