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Recently Adopted Accounting Pronouncements - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]    
Marketable securities $ 4,308  
ASU 2016-18 [Member]    
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]    
New accounting pronouncement or change in accounting principle, cumulative effect of change on equity or net assets 1,300 $ 1,200
ASU 2016-01 [Member]    
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]    
Marketable securities 4,300  
ASU 2016-01 [Member] | Maximum [Member]    
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]    
Gain on change in fair value of marketable securities $ 100