Annual report pursuant to Section 13 and 15(d)

Major Customers, Partnerships and Strategic Alliances - California Institute for Regenerative Medicine - Additional Information (Detail)

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Major Customers, Partnerships and Strategic Alliances - California Institute for Regenerative Medicine - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 12 Months Ended
May 31, 2014
May 31, 2013
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Research and Development Arrangement, Contract to Perform for Others [Line Items]          
Research grants     $ 508 $ 1,695 $ 1,990
California Institute for Regenerative Medicine [Member]          
Research and Development Arrangement, Contract to Perform for Others [Line Items]          
Funds due under the agreement $ 5,600        
Agreement to receive 4 years        
Research grants     0 0 0
Collaboration agreement related costs and expenses     1,600 1,700 1,800
California Institute for Regenerative Medicine [Member] | Beta-thalassemia [Member]          
Research and Development Arrangement, Contract to Perform for Others [Line Items]          
Funds due under the agreement   $ 6,400      
Agreement to receive   4 years      
Research grants     0 1,200 1,400
Collaboration agreement related costs and expenses     $ 0 1,200 $ 1,100
Unused funds received       $ 3,000