Investment Securities Available for Sale - Investments Gross Unrealized Losses and Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 100,097	$ 145,179
Less than 12 months, Unrealized Losses	4	458
12 months or more, Fair Value		117,903
12 months or more, Unrealized Losses		994
Total, Fair Value	100,097	263,082
Total, Unrealized Losses	4	1,452
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	99,997
Less than 12 months, Unrealized Losses	4
Total, Fair Value	99,997
Total, Unrealized Losses	4
Obligations of U.S. Government Sponsored Entities and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value		19,930
Less than 12 months, Unrealized Losses		70
Total, Fair Value		19,930
Total, Unrealized Losses		70
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	100	125,249
Less than 12 months, Unrealized Losses		388
12 months or more, Fair Value		117,903
12 months or more, Unrealized Losses		994
Total, Fair Value	$ 100	243,152
Total, Unrealized Losses		$ 1,382