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GOODWILL AND OTHER INTANGIBLE ASSETS, NET - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Aug. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]          
Goodwill   $ 37,144,000   $ 37,144,000  
Goodwill write-off $ 0        
Aggregate amortization expense   $ 843,000 $ 1,090,000    
Commercial Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill         $ 37,100,000
Mortgage Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill         $ 2,100,000
Goodwill write-off       $ 2,100,000  
Trade name intangibles          
Finite-Lived Intangible Assets [Line Items]          
Intangible asset write-off     90,000    
Core deposit intangibles          
Finite-Lived Intangible Assets [Line Items]          
Weighted average amortization period   5 years 10 months 1 day      
Core deposit intangibles | Minimum          
Finite-Lived Intangible Assets [Line Items]          
Amortization period of other intangible assets   4 years      
Core deposit intangibles | Maximum          
Finite-Lived Intangible Assets [Line Items]          
Amortization period of other intangible assets   10 years      
Customer relationship intangible          
Finite-Lived Intangible Assets [Line Items]          
Intangible asset write-off     $ 246,000