Summary of Borrowings (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Oct. 23, 2017
Debt Instrument [Line Items]
Principal amount	$ 104,700
Note payable to related party - net carrying amount	72,143	$ 79,666
Total debt - net carrying amount	105,478	156,822
Senior convertible notes due December 31, 2019
Debt Instrument [Line Items]
Principal amount	12,000
Senior convertible notes due December 31, 2019 \| Tranche B Notes
Debt Instrument [Line Items]
Principal amount	14,495	54,407
Unamortized debt issuance costs and debt (discount) premium	(293)	(1,662)
Net carrying amount	14,202	52,745
5.75% Senior convertible notes due October 23, 2021
Debt Instrument [Line Items]
Principal amount	18,690	23,690	$ 23,700
Unamortized debt issuance costs and debt (discount) premium	443	721
Net carrying amount	$ 19,133	$ 24,411

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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