Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stockholders Equity Note [Line Items]
Beginning Balance			$ 112,851
Issuance of common stock pursuant to ARIAD stock plans			2,344
Issuance of common stock, net of issuance costs			310,037
Stock-based compensation			19,928
Payment of tax withholding obligations related to stock- based compensation			(1,753)
Net change in unrealized gains on marketable securities			(12)
Cumulative translation adjustment	(26)		(26)
Net loss	(68,985)	(51,312)	(133,655)	(107,206)
Ending Balance	309,714		309,714
Common stock
Stockholders Equity Note [Line Items]
Beginning Balance (in shares)			167,075,758
Beginning Balance			167
Issuance of common stock pursuant to ARIAD stock plans (in shares)			1,210,272
Issuance of common stock pursuant to ARIAD stock plans			1
Issuance of common stock, net of issuance costs (in shares)			16,489,893
Issuance of common stock, net of issuance costs			17
Ending Balance (in shares)	184,775,923		184,775,923
Ending Balance	185		185
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Beginning Balance			890,499
Issuance of common stock pursuant to ARIAD stock plans			2,343
Issuance of common stock, net of issuance costs			310,020
Stock-based compensation			19,928
Payment of tax withholding obligations related to stock- based compensation			(1,753)
Ending Balance	1,221,037		1,221,037
Accumulated Other Comprehensive Income (Loss)
Stockholders Equity Note [Line Items]
Beginning Balance			20
Net change in unrealized gains on marketable securities			(12)
Cumulative translation adjustment	(26)		(26)
Ending Balance	(18)		(18)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Beginning Balance			(777,835)
Net loss			(133,655)
Ending Balance	$ (911,490)		$ (911,490)