Quarterly Financial Data - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Mar. 05, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014
Quarterly Financial Information [Line Items]
In-process research and development	$ 199,300			$ 220,766
In-process research and development credit		$ 3,900
Sirna Therapeutics
Quarterly Financial Information [Line Items]
In-process research and development			$ 224,700	$ 220,800
In-process research and development credit		$ 3,900