Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Exclusive of National Financial Instruments Measured at Fair Value on Recurring Basis (Detail)

v3.19.1
Fair Value Measurements - Exclusive of National Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Assets    
Long-term investments, at fair value   $ 1,390
Total   1,390
Liabilities    
Liabilities $ 10,905 15,068
Warrant [Member]    
Liabilities    
Liabilities 991 309
Helocyte Convertible Note One [Member]    
Liabilities    
Liabilities 0 4,700
Caelum Convertible Notes [Member]    
Liabilities    
Liabilities 9,914 10,059
Fair Value, Inputs, Level 1 [Member]    
Assets    
Long-term investments, at fair value   0
Total   0
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 1 [Member] | Warrant [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 1 [Member] | Helocyte Convertible Note One [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 1 [Member] | Caelum Convertible Notes [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 2 [Member]    
Assets    
Long-term investments, at fair value   0
Total   0
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 2 [Member] | Warrant [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 2 [Member] | Helocyte Convertible Note One [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 2 [Member] | Caelum Convertible Notes [Member]    
Liabilities    
Liabilities 0 0
Fair Value, Inputs, Level 3 [Member]    
Assets    
Long-term investments, at fair value   1,390
Total   1,390
Liabilities    
Liabilities 10,905 15,068
Fair Value, Inputs, Level 3 [Member] | Warrant [Member]    
Liabilities    
Liabilities 991 309
Fair Value, Inputs, Level 3 [Member] | Helocyte Convertible Note One [Member]    
Liabilities    
Liabilities 0 4,700
Fair Value, Inputs, Level 3 [Member] | Caelum Convertible Notes [Member]    
Liabilities    
Liabilities $ 9,914 $ 10,059