Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stockholders Equity Note [Line Items]
Beginning Balance			$ 185,517
Issuance of common stock pursuant to ARIAD stock plans			3,059
Stock-based compensation			24,583
Payment of tax withholding obligations related to stock-based compensation			(716)
Equity component of convertible debt			40,896
Purchase of convertible bond hedge			(43,220)
Sale of warrants			27,580
Net loss	(49,948)	(66,348)	(156,607)	(200,042)
Ending Balance	81,092		81,092
Common Stock
Stockholders Equity Note [Line Items]
Beginning Balance (in shares)			185,896,080
Beginning Balance			186
Issuance of common stock pursuant to ARIAD stock plans (in shares)			1,245,815
Issuance of common stock pursuant to ARIAD stock plans			1
Ending Balance (in shares)	187,141,895		187,141,895
Ending Balance	187		187
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Beginning Balance			1,238,859
Issuance of common stock pursuant to ARIAD stock plans			3,058
Stock-based compensation			24,583
Payment of tax withholding obligations related to stock-based compensation			(716)
Equity component of convertible debt			40,896
Purchase of convertible bond hedge			(43,220)
Sale of warrants			27,580
Ending Balance	1,291,040		1,291,040
Other Comprehensive Income (Loss)
Stockholders Equity Note [Line Items]
Beginning Balance			(1,535)
Net loss			244
Ending Balance	(1,291)		(1,291)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Beginning Balance			(1,051,993)
Net loss			(156,851)
Ending Balance	$ (1,208,844)		$ (1,208,844)