Quarterly report pursuant to Section 13 or 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 ($)
1 Months Ended 3 Months Ended 6 Months Ended
May 31, 2014
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]          
Research grants   $ 276,000 $ 110,000 $ 395,000 $ 341,000
California Institute for Regenerative Medicine [Member]          
Research and Development Arrangement, Contract to Perform for Others [Line Items]          
Funds due under the agreement $ 5,600,000        
Agreement to receive 4 years        
Research grants   0 0 0 0
Collaboration agreement related costs and expenses   $ 100,000 $ 400,000 $ 300,000 $ 700,000