Accounts Payable, Accrued Expenses and Other Current Liabilities - Components of Accounts Payable, Accrued Expenses and Other Current Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Clinical and preclinical	$ 32,381	$ 31,069
Royalties payable	13,554	13,582
Accrued professional services and other current liabilities	12,567	8,909
Accounts payable	12,212	10,492
Payroll and payroll-related	11,166	33,272
Other payable to licensor	5,949	5,000
Interest payable	3,396	1,698
Current portion of long-term debt	738	4
Taxes payable	2	2,106
Total	$ 91,965	$ 106,132