Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities Available for Sale, Additional Information (Detail) - USD ($) $ in Thousands |
Dec. 31, 2018 |
Dec. 31, 2017 |
---|---|---|
Investment Securities [Line Items] | ||
Amortized Cost | $ 924,054 | $ 740,846 |
Securities available for sale | 909,247 | $ 731,358 |
US Government Agencies Debt Securities [Member] | ||
Investment Securities [Line Items] | ||
Amortized Cost | 178,600 | |
Securities available for sale | 177,200 | |
Obligations of U.S. Government-Sponsored Enterprises [Member] | ||
Investment Securities [Line Items] | ||
Amortized Cost | 686,900 | |
Securities available for sale | $ 673,400 |