Organization and Significant Accounting Policies - Fair Value Measurement and Unobservable Rollforward Activity of Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Adjustments to estimated fair value	$ 597	$ 355
Warrants [Member]
Fair Value Disclosures [Abstract]
Beginning balance	1,745	$ 3,113	$ 3,113
Adjustments to estimated fair value	(597)		(1,368)
Ending balance	$ 1,148		$ 1,745

Amount of expense (income) related to adjustment to fair value of warrant liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 25
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=109262497&loc=d3e20148-110875

Name:	us-gaap_FairValueAdjustmentOfWarrants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration