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Fair Values of Financial Instruments - Summary of Information Regarding Changes in Fair Value of Assets Measured at Fair Value (Detail) - Fair Value, Inputs, Level 3 [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Balance, beginning of period $ 34  
Transfer into Level 3   $ 34
Unrealized loss on equity security (32)  
Sale of equity security $ (2)  
Balance, end of period   $ 34