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Commitments and Contingencies - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Apr. 03, 2018
Mar. 23, 2018
Mar. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Commitments And Contingencies [Line Items]          
Loss Contingency, Damages Sought, Value $ 5.0 $ 5.0      
Percentage Of Financial Guarantee Benchmark Amount     2.00%    
Standby Letters of Credit [Member]          
Commitments And Contingencies [Line Items]          
Long-term Line of Credit     $ 0.3    
Preferred Bank [Member]          
Commitments And Contingencies [Line Items]          
Long-term Line of Credit       $ 6.6 $ 6.7