Summary of Business and Significant Accounting Policies - Additional Information (Details) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Reportingunit shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)		Jan. 01, 2019 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net loss	$ (3,273)	$ (21,494)	$ (11,882)	$ (38,882)	$ (41,244)
Accumulated deficit	(276,595)		(276,595)		(264,713)	[1]
Cash, cash equivalents and restricted cash	$ 10,138	14,690	10,138	14,690	11,503			$ 28,837
Net proceeds from common stock sold			$ 1,504
Common stock sold under agreement | shares	0		570
Allowance for doubtful accounts	$ 1,891		$ 1,891		2,651
Allowance for potential customer revenue credits	298		$ 298		353
Number of reporting unit | Reportingunit			1
Impairment of goodwill	0	$ 14,740	$ 0	$ 14,740
Right-of-use assets	8,641		8,641		$ 0	[1]
Lease liability	9,990		9,990
ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets							$ 14,589
Lease liability							$ 16,425
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Aggregate offering price	50,000		50,000
JMP Securities [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Aggregate offering price	$ 13,000		$ 13,000

[1] Derived from the Company’s audited consolidated financial statements as of December 31, 2018.