Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stockholders Equity Note [Line Items]
Beginning Balance	$ 80,801
Issuance of common stock pursuant to ARIAD stock plans	1,321
Stock-based compensation	8,434
Payment of tax withholding obligations related to stock-based compensation	(130)
Other comprehensive income	313	40
Net loss	(52,676)	(49,822)
Ending Balance	38,063
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)	1,073,690
Issuance of common stock pursuant to ARIAD stock plans	1
Ending Balance (in shares)	188,367,784
Ending Balance	188
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Beginning Balance	1,299,394
Issuance of common stock pursuant to ARIAD stock plans	1,320
Stock-based compensation	8,434
Payment of tax withholding obligations related to stock-based compensation	(130)
Ending Balance	1,309,018
Accumulated Other Comprehensive Income
Stockholders Equity Note [Line Items]
Beginning Balance	(4,185)
Other comprehensive income	313
Ending Balance	(3,872)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Beginning Balance	(1,214,595)
Net loss	(52,676)
Ending Balance	$ (1,267,271)