Investments and Fair Value of Financial Instruments - Summary of Amortized Cost and Fair Value of the Available-For-Sale Investment Securities Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 17,281	$ 21,072
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	17,281	21,072
Cash Equivalents [Member] \| Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,283	9,902
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	6,283	9,902
Cash Equivalents [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,044	1,345
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	3,044	1,345
Cash Equivalents [Member] \| Corporate Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	599
Unrealized Gains	0
Unrealized Losses	0
Estimated Fair Value	599
Short-term Investments [Member] \| Treasury Bills [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	997	1,195
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	997	1,195
Short-term Investments [Member] \| Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,110	6,776
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	5,110	6,776
Short-term Investments [Member] \| Corporate Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,248	656
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	$ 1,248	656
Short-term Investments [Member] \| U.S. Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		1,198
Unrealized Gains		0
Unrealized Losses		0
Estimated Fair Value		$ 1,198

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-SubTopic 10
-Section 50
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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