Purchase Commitments - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Batch
Long Term Purchase Commitment [Line Items]
Accounts payables	$ 9,487,000	$ 14,546,000
Accrued research and development	11,169,000	23,818,000
Prepaid research and development	5,898,000	7,299,000
Prepaid and other long-term assets	$ 4,168,000	$ 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	3,800,000
Accounts payables	1,000,000
Accrued research and development	100,000
Prepaid manufacturing services	2,300,000
Hovione, Limited
Long Term Purchase Commitment [Line Items]
Prepaid research and development	2,000,000
Prepaid and other long-term assets	4,100,000
Hovione, Limited | Maximum
Long Term Purchase Commitment [Line Items]
Cancellable additional purchase commitments	$ 22,100,000