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Financial Instruments - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2015
Financial Instruments [Line Items]        
Period cash equivalents and short-term investments have been in continuous unrealized 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       $ 95,000,000
Cash collateral percentage 100.00%      
Credit facility borrowings $ 0   $ 0  
Revolving credit facility maturity date Dec. 31, 2018      
CCKF [Member]        
Financial Instruments [Line Items]        
Percentage of investment in equity affiliate 30.70%      
Non controlling interest $ 3,400,000      
Loss from investment in affiliate $ 100,000 $ (200,000)