Purchase Commitments - Additional Information (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) Batch
Long Term Purchase Commitment [Line Items]
Accounts payables	$ 17,463,000	$ 17,463,000	$ 14,546,000
Prepaid expenses and other current assets	8,766,000	8,766,000	2,680,000
Prepaid and other long-term assets	9,609,000	$ 9,609,000	$ 5,214,000
CMC ICOS Biologics Inc
Long Term Purchase Commitment [Line Items]
Number of batches to be manufactured, 2017 | Batch			20
Non-refundable manufacturing reservation payments committed			$ 2,500,000
Purchase commitment, description		We have made firm orders to manufacture 20 batches in 2017 and are required to make a non-refundable manufacturing reservation payment of $2.5 million for ten batches to be manufactured in 2018 contingent upon CMC’s successful delivery of services related to our BLA re-submission to the FDA
Number of batches to be manufactured, 2018 | Batch			10
Purchase obligation services received		$ 33,700,000
Repayment of accounts payable and accrued liabilities	2,000,000	7,300,000
Accounts payables	500,000	500,000
Prepaid manufacturing services	500,000	500,000
Hovione, Limited
Long Term Purchase Commitment [Line Items]
Prepaid expenses and other current assets	2,700,000	2,700,000
Prepaid and other long-term assets	$ 9,600,000	9,600,000
Hovione, Limited | Maximum
Long Term Purchase Commitment [Line Items]
Cancellable and non-cancellable additional purchase commitments		$ 12,900,000