License Obligations - Evonik Definitive Development and Exclusive License Option Agreement - Additional Information (Detail) - Development and Exclusive License Option Agreement [Member] $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of license agreements granted | Agreement	2
Expenses and development service fees payable	$ 2,160
Expenses and development service fees paid	$ 2,000