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Investments - Additional Information (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]    
Cash and cash equivalents $ 69.8 $ 55.6
Held-to-Maturity Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Investments $ 10.1 $ 30.1