Quarterly report pursuant to Section 13 or 15(d)

Securities - Available for Sale Securities, Continuous Unrealized Loss Position, Fair value (Detail)

v3.10.0.1
Securities - Available for Sale Securities, Continuous Unrealized Loss Position, Fair value (Detail)
$ in Thousands
Sep. 30, 2018
USD ($)
Security
Dec. 31, 2017
USD ($)
Security
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 4,858 $ 2,691
Available-for-Sale Within One Year, Estimated Fair Value $ 273,851 $ 276,372
Available-for-Sale Within One Year, Number of Securities | Security 99 93
Available-for-Sale More than One Year, Gross Unrealized Loss $ 11,069 $ 2,593
Available-for-Sale More than One Year, Estimated Fair Value $ 287,660 $ 138,033
Available-for-Sale More than One Year, Number of Securities | Security 126 67
Available-for-Sale, Gross Unrealized Loss $ 15,927 $ 5,284
Available-for-Sale, Estimated Fair Value $ 561,511 $ 414,405
Available-for-Sale, Number of Securities | Security 225 160
Mortgage-backed securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 2,484 $ 1,855
Available-for-Sale Within One Year, Estimated Fair Value $ 109,384 $ 197,621
Available-for-Sale Within One Year, Number of Securities | Security 44 66
Available-for-Sale More than One Year, Gross Unrealized Loss $ 7,235 $ 847
Available-for-Sale More than One Year, Estimated Fair Value $ 183,568 $ 56,998
Available-for-Sale More than One Year, Number of Securities | Security 72 25
Available-for-Sale, Gross Unrealized Loss $ 9,719 $ 2,702
Available-for-Sale, Estimated Fair Value $ 292,952 $ 254,619
Available-for-Sale, Number of Securities | Security 116 91
Collateralized mortgage obligations [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 453 $ 773
Available-for-Sale Within One Year, Estimated Fair Value $ 26,235 $ 65,726
Available-for-Sale Within One Year, Number of Securities | Security 7 20
Available-for-Sale More than One Year, Gross Unrealized Loss $ 3,439 $ 1,125
Available-for-Sale More than One Year, Estimated Fair Value $ 89,706 $ 49,986
Available-for-Sale More than One Year, Number of Securities | Security 47 32
Available-for-Sale, Gross Unrealized Loss $ 3,892 $ 1,898
Available-for-Sale, Estimated Fair Value $ 115,941 $ 115,712
Available-for-Sale, Number of Securities | Security 54 52
U.S. government agency securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 0 $ 15
Available-for-Sale Within One Year, Estimated Fair Value $ 0 $ 1,484
Available-for-Sale Within One Year, Number of Securities | Security 0 1
Available-for-Sale More than One Year, Gross Unrealized Loss $ 147 $ 70
Available-for-Sale More than One Year, Estimated Fair Value $ 7,352 $ 5,930
Available-for-Sale More than One Year, Number of Securities | Security 3 2
Available-for-Sale, Gross Unrealized Loss $ 147 $ 85
Available-for-Sale, Estimated Fair Value $ 7,352 $ 7,414
Available-for-Sale, Number of Securities | Security 3 3
Municipal bonds-tax exempt [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 1,811 $ 48
Available-for-Sale Within One Year, Estimated Fair Value $ 98,667 $ 11,541
Available-for-Sale Within One Year, Number of Securities | Security 43 6
Available-for-Sale More than One Year, Gross Unrealized Loss $ 248 $ 21
Available-for-Sale More than One Year, Estimated Fair Value $ 7,034 $ 2,737
Available-for-Sale More than One Year, Number of Securities | Security 4 2
Available-for-Sale, Gross Unrealized Loss $ 2,059 $ 69
Available-for-Sale, Estimated Fair Value $ 105,701 $ 14,278
Available-for-Sale, Number of Securities | Security 47 8
U.S treasury securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 110  
Available-for-Sale Within One Year, Estimated Fair Value $ 39,565  
Available-for-Sale Within One Year, Number of Securities | Security 5  
Available-for-Sale More than One Year, Gross Unrealized Loss $ 0  
Available-for-Sale More than One Year, Estimated Fair Value $ 0  
Available-for-Sale More than One Year, Number of Securities | Security 0  
Available-for-Sale, Gross Unrealized Loss $ 110  
Available-for-Sale, Estimated Fair Value $ 39,565  
Available-for-Sale, Number of Securities | Security 5  
Mutual funds [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss   $ 0
Available-for-Sale Within One Year, Estimated Fair Value   $ 0
Available-for-Sale Within One Year, Number of Securities | Security   0
Available-for-Sale More than One Year, Gross Unrealized Loss   $ 530
Available-for-Sale More than One Year, Estimated Fair Value   $ 22,382
Available-for-Sale More than One Year, Number of Securities | Security   6
Available-for-Sale, Gross Unrealized Loss   $ 530
Available-for-Sale, Estimated Fair Value   $ 22,382
Available-for-Sale, Number of Securities | Security   6