Lease liabilities - Schedule of Company's Operating and Finance Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finance lease liability
December 31, 2019	$ 2
December 31, 2020	67
December 31, 2021	60
December 31, 2022	60
December 31, 2023	59
Total undiscounted lease payments	248
Less: imputed interest	(37)
Total lease liabilities	211
Less: current portion	(65)	$ (9)
Non-current lease liabilities – September 30, 2019	146	$ 6
Operating lease liability
December 31, 2019	51
December 31, 2020	207
December 31, 2021	172
Total undiscounted lease payments	430
Less: imputed interest	(25)
Total lease liabilities	405
Less: current portion	(200)
Non-current lease liabilities – September 30, 2019	$ 205