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
Jun. 30, 2018
USD ($)
Security
Dec. 31, 2017
USD ($)
Security
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 9,027 $ 2,691
Available-for-Sale Within One Year, Estimated Fair Value $ 412,019 $ 276,372
Available-for-Sale Within One Year, Number of Securities | Security 144 93
Available-for-Sale More than One Year, Gross Unrealized Loss $ 4,147 $ 2,593
Available-for-Sale More than One Year, Estimated Fair Value $ 126,945 $ 138,033
Available-for-Sale More than One Year, Number of Securities | Security 72 67
Available-for-Sale, Gross Unrealized Loss $ 13,174 $ 5,284
Available-for-Sale, Estimated Fair Value $ 538,964 $ 414,405
Available-for-Sale, Number of Securities | Security 216 160
Mortgage-backed securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 6,475 $ 1,855
Available-for-Sale Within One Year, Estimated Fair Value $ 266,671 $ 197,621
Available-for-Sale Within One Year, Number of Securities | Security 90 66
Available-for-Sale More than One Year, Gross Unrealized Loss $ 1,801 $ 847
Available-for-Sale More than One Year, Estimated Fair Value $ 55,820 $ 56,998
Available-for-Sale More than One Year, Number of Securities | Security 29 25
Available-for-Sale, Gross Unrealized Loss $ 8,276 $ 2,702
Available-for-Sale, Estimated Fair Value $ 322,491 $ 254,619
Available-for-Sale, Number of Securities | Security 119 91
Collateralized mortgage obligations [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 1,259 $ 773
Available-for-Sale Within One Year, Estimated Fair Value $ 56,947 $ 65,726
Available-for-Sale Within One Year, Number of Securities | Security 14 20
Available-for-Sale More than One Year, Gross Unrealized Loss $ 2,120 $ 1,125
Available-for-Sale More than One Year, Estimated Fair Value $ 62,593 $ 49,986
Available-for-Sale More than One Year, Number of Securities | Security 39 32
Available-for-Sale, Gross Unrealized Loss $ 3,379 $ 1,898
Available-for-Sale, Estimated Fair Value $ 119,540 $ 115,712
Available-for-Sale, Number of Securities | Security 53 52
U.S. government agency securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 44 $ 15
Available-for-Sale Within One Year, Estimated Fair Value $ 1,455 $ 1,484
Available-for-Sale Within One Year, Number of Securities | Security 1 1
Available-for-Sale More than One Year, Gross Unrealized Loss $ 95 $ 70
Available-for-Sale More than One Year, Estimated Fair Value $ 5,905 $ 5,930
Available-for-Sale More than One Year, Number of Securities | Security 2 2
Available-for-Sale, Gross Unrealized Loss $ 139 $ 85
Available-for-Sale, Estimated Fair Value $ 7,360 $ 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 $ 1,249 $ 48
Available-for-Sale Within One Year, Estimated Fair Value $ 86,946 $ 11,541
Available-for-Sale Within One Year, Number of Securities | Security 39 6
Available-for-Sale More than One Year, Gross Unrealized Loss $ 131 $ 21
Available-for-Sale More than One Year, Estimated Fair Value $ 2,627 $ 2,737
Available-for-Sale More than One Year, Number of Securities | Security 2 2
Available-for-Sale, Gross Unrealized Loss $ 1,380 $ 69
Available-for-Sale, Estimated Fair Value $ 89,573 $ 14,278
Available-for-Sale, Number of Securities | Security 41 8
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