Development and License Agreements - Summary of Amounts Payable and Amounts Receivable from Fresenius (Detail) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Related Party Transactions [Abstract]
Payables to Fresenius	[1]	$ 6,198	$ 4,687
Receivables from Fresenius	[2]	$ 1,714	$ 231

[1] Included in “Accounts Payable” and “Accrued Liabilities” in the Company's consolidated balance sheets.

[2] Included in “Other current assets” in the Company's consolidated balance sheets