Summary Of Significant Accounting Policies - Schedule Of Impact Of Accompanying Consolidated Statement of Balance Sheet (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Jan. 01, 2019		Dec. 31, 2018
Assets:
Operating lease right-of-use assets		$ 1,993	$ 1,301		$ 0
Operating lease liabilities:
Accrued and other current liabilities		17,597	13,924	[1]	12,969	[1]
Other non-current liabilities		$ 1,455	733	[2]	$ 387	[2]
Accounting Standards Update 2016-02 [Member]
Assets:
Operating lease right-of-use assets			1,301
Accounting Standards Update 2016-02 [Member] | Accrued and other current liabilities [Member]
Operating lease liabilities:
Accrued and other current liabilities	[1]		955
Accounting Standards Update 2016-02 [Member] | Other non-current liabilities [Member]
Operating lease liabilities:
Other non-current liabilities	[2]		$ 346

[1] Includes deferred rent and current portion of operating lease liabilities

[2] Includes deferred rent and non-current portion of operating lease liabilities