Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

Name:	us-gaap_CashCashEquivalentsAndShortTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Notes Payable - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Dec. 29, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Proceeds from issuance of notes payable	$ 20,000,000
Unrestricted cash, cash equivalents and marketable securities		$ 82,000,000		$ 82,000,000
Credit facility default amount		300,000		300,000
Maximum [Member]
Debt Instrument [Line Items]
Aggregate value of cash maintained by Australian subsidiary, limit				4,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowings under term loan	$ 20,000,000	$ 16,400,000		$ 16,400,000
Debt facility description				Upon entering into the Term Loan, the Company became obligated to make monthly, interest-only payments until March 29, 2019 and, thereafter, to pay 33 consecutive, equal monthly installments of principal and interest from April 1, 2019 through December 1, 2021. The outstanding Term Loan bears a variable interest at an annual rate of 1.25% above the prime rate, which at September 30, 2019 was 5.0%. In addition, a final payment equal to 8.0% of the Term Loan is due upon the earlier of the maturity date, acceleration of the Term Loan or prepayment of all or part of the Term Loan.
Debt maturity date	Dec. 01, 2021
Debt facility interest rate description				1.25% above the prime rate
Debt facility variable interest at annual rate	1.25%
Debt facility effective interest rate		5.00%		5.00%
Debt facility fee percentage	8.00%
Charges to interest expense of debt outstanding	$ 1,600,000
Loan agreement minimum liquidity required		$ 17,200,000		$ 17,200,000		$ 21,000,000
Debt facility covenant description				Further, from 45 days after the Term Loan was entered in, the Company has met its obligation to maintain a balance of unrestricted cash, cash equivalents and marketable securities at Silicon Valley Bank in an amount not less than the greater of (i) $55.0 million and (ii) sixty-five percent (65%) of all the Company’s cash, cash equivalents and marketable securities. If the Company does not meet this requirement it will not be considered an event of default provided it immediately secures 87.5% of the principal balance in a restricted cash account.
Percentage of principal balance to be secured in restricted cash account for not to be considered an event of default				87.50%
Interest expense on term loan		400,000	$ 500,000	$ 1,400,000	$ 1,400,000
Debt facility effective interest rate				9.40%
Term Loan [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Percentage equivalent of cash, cash equivalents and marketable securities balance				105.00%
Unrestricted cash, cash equivalents and marketable securities		$ 55,000,000		$ 55,000,000
Percentage of cash, cash equivalents and marketable securities		65.00%		65.00%