Changes in Stockholders' Equity (Deficit) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stockholders Equity Note [Line Items]
Beginning Balance			$ 80,801
Issuance of common stock pursuant to ARIAD stock plans			3,598
Stock-based compensation			29,009
Payment of tax withholding obligations related to stock-based compensation			(321)
Other comprehensive income	$ 8,807	$ 160	8,548	$ 244
Net loss	(55,451)	$ (50,108)	(171,285)	$ (156,851)
Ending Balance	$ (49,650)		$ (49,650)
Common Stock
Stockholders Equity Note [Line Items]
Beginning Balance (in shares)			187,294,094
Beginning Balance			$ 187
Issuance of common stock pursuant to ARIAD stock plans (in shares)			1,895,796
Issuance of common stock pursuant to ARIAD stock plans			$ 2
Ending Balance (in shares)	189,189,890		189,189,890
Ending Balance	$ 189		$ 189
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Beginning Balance			1,299,394
Issuance of common stock pursuant to ARIAD stock plans			3,596
Stock-based compensation			29,009
Payment of tax withholding obligations related to stock-based compensation			(321)
Ending Balance	1,331,678		1,331,678
Accumulated Other Comprehensive Income
Stockholders Equity Note [Line Items]
Beginning Balance			(4,185)
Other comprehensive income			8,548
Ending Balance	4,363		4,363
Accumulated Deficit
Stockholders Equity Note [Line Items]
Beginning Balance			(1,214,595)
Net loss			(171,285)
Ending Balance	$ (1,385,880)		$ (1,385,880)