Commercial Supply Agreement - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Jul. 31, 2014	Sep. 30, 2015	Dec. 31, 2014	Nov. 01, 2014
Long Term Purchase Commitment [Line Items]
Prepaid and other long-term assets		$ 12,987,000	$ 15,612,000
Prepaid expenses and other current assets		20,499,000	$ 5,747,000
CMC ICOS Biologics Inc
Long Term Purchase Commitment [Line Items]
Commercial supply agreement upfront payment	$ 10,000,000
Commercial supply (manufacturing services) agreement reservation payment				$ 4,600,000
Commercial agreement fixed commitment amount	293,900,000
Payments made for purchases of batches related to commercial supply agreement		$ 18,700,000
Term of commercial supply agreement		7 years
Purchases of batches recorded in prepaid expenses and other current assets		$ 14,100,000
CMC ICOS Biologics Inc | Upfront and Reservation Payment
Long Term Purchase Commitment [Line Items]
Prepaid expenses and other assets		14,600,000
Prepaid and other long-term assets		12,300,000
Prepaid expenses and other current assets		$ 2,300,000
CMC ICOS Biologics Inc | Minimum
Long Term Purchase Commitment [Line Items]
Termination fees payment under obligation	5,000,000
CMC ICOS Biologics Inc | Maximum
Long Term Purchase Commitment [Line Items]
Termination fees payment under obligation	$ 30,000,000