Commercial Supply Agreement - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 31, 2014	Jun. 30, 2015	Dec. 31, 2014	Nov. 01, 2014
Long Term Purchase Commitment [Line Items]
Prepaid and other long-term assets		$ 13,910	$ 15,612
Prepaid expenses and other current assets		15,967	$ 5,747
CMC ICOS Biologics Inc
Long Term Purchase Commitment [Line Items]
Commercial supply agreement upfront payment	$ 10,000
Commercial supply (manufacturing services) agreement reservation payment				$ 4,600
Commercial agreement fixed commitment amount	293,900
Payments made for purchases of batches related to commercial supply agreement		$ 10,600
Term of commercial supply agreement		7 years
Purchases of batches recorded in prepaid expenses and other current assets		$ 9,500
CMC ICOS Biologics Inc | Upfront Fee
Long Term Purchase Commitment [Line Items]
Prepaid expenses and other assets		14,600
Prepaid and other long-term assets		13,100
Prepaid expenses and other current assets		$ 1,500
CMC ICOS Biologics Inc | Minimum
Long Term Purchase Commitment [Line Items]
Termination fees payment under obligation	5,000
CMC ICOS Biologics Inc | Maximum
Long Term Purchase Commitment [Line Items]
Termination fees payment under obligation	$ 30,000