Significant Agreements - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Significant Agreements [Line Items]
Milestone fee upon submission of preclinical regulatory filings									$ 500
Milestone fee upon commencement of clinical trials in humans									24,700
Milestone fee upon submission of regulatory approval filings									40,000
Milestone fee upon approval of commercial products by regulatory agencies									97,500
Milestone fee upon achievement of specified sales targets for licensed products									92,000
Research and development (including amounts to related parties)	$ 16,059	$ 12,560	$ 10,680	$ 6,183	$ 4,812	$ 5,664	$ 4,012	$ 2,791	$ 45,482		$ 17,279	$ 4,961
MeuSIX [Member]
Significant Agreements [Line Items]
Percentage of reimbursed by grantor									75.00%	75.00%
Maximum amount of reimbursed cost recognized for grant | €										€ 2,300,000
Period of grant									5 years	5 years
Research and development (including amounts to related parties)									$ 200		900	1,100
Grant revenue									100		300	$ 800
Accounts receivable	$ 600				$ 500				$ 600		$ 500