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Financial Instruments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Dec. 27, 2018
Financial Instruments [Line Items]            
Period cash equivalents and short-term investments have been in continuous unrealized gain (loss) position, years, maximum     1 year      
Credit Agreement [Member] | Revolving Credit Facility [Member] | BMO Harris Bank N.A. ("BMO Harris") [Member]            
Financial Instruments [Line Items]            
Revolving credit facility           $ 50,000,000.0
Percentage of cash and marketable securities deposited with bank collateral for securitization 100.00%   100.00%      
Credit facility borrowings $ 0   $ 0   $ 0  
Revolving credit facility maturity date     Jan. 20, 2022      
CCKF [Member]            
Financial Instruments [Line Items]            
Percentage of investment in equity affiliate 30.70%   30.70%      
Non controlling interest $ 2,600,000   $ 2,600,000      
Gain (loss) from investment in affiliate       $ (100,000)    
CCKF [Member] | Maximum [Member]            
Financial Instruments [Line Items]            
Gain (loss) from investment in affiliate $ 100,000 $ 100,000 $ 100,000