Deposits - Summary of Interest Expense on Deposits (Detail) - USD ($) $ in Thousands  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017  | 
Dec. 31, 2016  | 
Dec. 31, 2015  | 
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| Banking and Thrift [Abstract] | |||
| Demand – interest-bearing | $ 74 | $ 75 | $ 114 | 
| Money market and savings | 12,515 | 6,470 | 4,195 | 
| Time deposits of $100,000 or more | 10,471 | 6,605 | 6,639 | 
| Other time deposits | 3,029 | 3,420 | 4,462 | 
| Total interest expense on deposits | $ 26,089 | $ 16,570 | $ 15,410 | 
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- References No definition available. 
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- Definition Aggregate amount of interest expense on all deposits. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The aggregate interest expense incurred on the following for deposits in domestic offices: (1) transaction accounts (NOW, and telephone and preauthorized transfer accounts), (2) money market deposits and (3) savings deposits. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Interest expense incurred on other deposits in domestic offices. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Interest expense incurred on all savings account deposits. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Interest expense incurred on time deposits, including certificates of deposits, of $100,000 or more in domestic offices. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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