Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stockholders Equity Note [Line Items]
Beginning Balance			$ 185,517
Issuance of common stock pursuant to ARIAD stock plans			2,263
Stock-based compensation			16,945
Payment of tax withholding obligations related to stock-based compensation			(558)
Equity component of convertible debt			40,896
Purchase of convertible bond hedge			(43,220)
Sale of warrants			27,580
Net loss	(56,877)	(69,041)	(106,659)	(133,693)
Ending Balance	122,764		122,764
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)			966,397
Issuance of common stock pursuant to ARIAD stock plans			1
Ending Balance (in shares)	186,862,477		186,862,477
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			2,262
Stock-based compensation			16,945
Payment of tax withholding obligations related to stock-based compensation			(558)
Equity component of convertible debt			40,896
Purchase of convertible bond hedge			(43,220)
Sale of warrants			27,580
Ending Balance	1,282,764		1,282,764
Accumulated Other Comprehensive Income
Stockholders Equity Note [Line Items]
Beginning Balance			(1,535)
Net loss			84
Ending Balance	(1,451)		(1,451)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Beginning Balance			(1,051,993)
Net loss			(106,743)
Ending Balance	$ (1,158,736)		$ (1,158,736)