License Agreements - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Feb. 28, 2014	Dec. 31, 2014
Other Commitments [Line Items]
Litigation expense for legal reimbursements	$ 691,000	$ 1,990,000
Fred Hutchinson Cancer Research Center [Member]
Other Commitments [Line Items]
Minimum annual royalty payment after year five	100,000
Notice period for agreement termination	90 days
Fred Hutchinson Cancer Research Center [Member] | Maximum [Member]
Other Commitments [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	6,750,000
Memorial Sloan Kettering Cancer Center [Member]
Other Commitments [Line Items]
Minimum annual royalty payment after year five	100,000
Notice period for agreement termination	30 days
Memorial Sloan Kettering Cancer Center [Member] | Maximum [Member]
Other Commitments [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	6,750,000
St. Jude Children's Research Hospital [Member]
Other Commitments [Line Items]
Litigation expense for legal reimbursements	200,000	500,000
Minimum annual royalty payment in year one	100,000
Minimum annual royalty payment in year two	100,000
Minimum annual royalty payment after year two	500,000
St. Jude Children's Research Hospital [Member] | Maximum [Member]
Other Commitments [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	62,500,000
Seattle Children's Research Institute [Member]
Other Commitments [Line Items]
Notice period for agreement termination			60 days
Upfront license fee paid		200,000
Minimum annual license maintenance payment in year one			50,000
Minimum annual license maintenance payment in year two			50,000
Minimum annual license maintenance payment in year three			50,000
Minimum annual license maintenance payment in year four			50,000
Minimum annual license maintenance payment in year five			50,000
Minimum annual license maintenance payment after year five			200,000
Seattle Children's Research Institute [Member] | Maximum [Member]
Other Commitments [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	9,000,000
Opus Bio [Member]
Other Commitments [Line Items]
Notice period for agreement termination				30 days
Milestone payments payable in shares of common stock				52,500,000
Share price used in milestone payments payable in shares of common stock calculation				$ 10.92
Maximum shares for milestone payments payable in shares of common stock				4,807,692
Trading period used in milestone payments payable in shares of common stock calculation				30 days
Development and commercialization expenses				2,500,000
Opus Bio [Member] | Maximum [Member]
Other Commitments [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	215,000,000
Pass-through payments owed by counter party	$ 2,800,000