Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Securities - Available for Sale Securities, Continuous Unrealized Loss Position, Fair value (Detail)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Security
Dec. 31, 2017
USD ($)
Security
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 8,532 $ 2,691
Available-for-Sale Within One Year, Estimated Fair Value $ 399,643 $ 276,372
Available-for-Sale Within One Year, Number of Securities | Security 142 93
Available-for-Sale More than One Year, Gross Unrealized Loss $ 3,224 $ 2,593
Available-for-Sale More than One Year, Estimated Fair Value $ 114,722 $ 138,033
Available-for-Sale More than One Year, Number of Securities | Security 68 67
Available-for-Sale, Gross Unrealized Loss $ 11,756 $ 5,284
Available-for-Sale, Estimated Fair Value $ 514,365 $ 414,405
Available-for-Sale, Number of Securities | Security 210 160
Mortgage-backed securities [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 5,777 $ 1,855
Available-for-Sale Within One Year, Estimated Fair Value $ 243,061 $ 197,621
Available-for-Sale Within One Year, Number of Securities | Security 83 66
Available-for-Sale More than One Year, Gross Unrealized Loss $ 1,446 $ 847
Available-for-Sale More than One Year, Estimated Fair Value $ 54,871 $ 56,998
Available-for-Sale More than One Year, Number of Securities | Security 28 25
Available-for-Sale, Gross Unrealized Loss $ 7,223 $ 2,702
Available-for-Sale, Estimated Fair Value $ 297,932 $ 254,619
Available-for-Sale, Number of Securities | Security 111 91
Collateralized mortgage obligations [Member]    
Summary of Investment Holdings [Line Items]    
Available-for-Sale Within One Year, Gross Unrealized Loss $ 1,388 $ 773
Available-for-Sale Within One Year, Estimated Fair Value $ 65,798 $ 65,726
Available-for-Sale Within One Year, Number of Securities | Security 18 20
Available-for-Sale More than One Year, Gross Unrealized Loss $ 1,557 $ 1,125
Available-for-Sale More than One Year, Estimated Fair Value $ 51,314 $ 49,986
Available-for-Sale More than One Year, Number of Securities | Security 36 32
Available-for-Sale, Gross Unrealized Loss $ 2,945 $ 1,898
Available-for-Sale, Estimated Fair Value $ 117,112 $ 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 $ 36 $ 15
Available-for-Sale Within One Year, Estimated Fair Value $ 1,464 $ 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 $ 131 $ 85
Available-for-Sale, Estimated Fair Value $ 7,369 $ 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 $ 1,331 $ 48
Available-for-Sale Within One Year, Estimated Fair Value $ 89,320 $ 11,541
Available-for-Sale Within One Year, Number of Securities | Security 40 6
Available-for-Sale More than One Year, Gross Unrealized Loss $ 126 $ 21
Available-for-Sale More than One Year, Estimated Fair Value $ 2,632 $ 2,737
Available-for-Sale More than One Year, Number of Securities | Security 2 2
Available-for-Sale, Gross Unrealized Loss $ 1,457 $ 69
Available-for-Sale, Estimated Fair Value $ 91,952 $ 14,278
Available-for-Sale, Number of Securities | Security 42 8
Municipal bonds-taxable [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   $ 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   $ 0
Available-for-Sale, Estimated Fair Value   $ 0
Available-for-Sale, Number of Securities | Security   0
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