Investment Securities - Schedule of Securities Classified as Available-for-Sale with Gross Unrealized Losses Aggregated by Category and Length of Time (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	$ 124,122	$ 742,044
Losses less than 12 Months, Gross Unrealized Losses	1,233	4,675
Losses more than 12 Months, Estimated Fair Value	23,039	75,209
Losses more than 12 Months, Gross Unrealized Losses	547	794
Obligations of U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	29,360	33,053
Losses less than 12 Months, Gross Unrealized Losses	278	209
Losses more than 12 Months, Estimated Fair Value	12,896	13,703
Losses more than 12 Months, Gross Unrealized Losses	180	206
MBS
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	72,267	708,991
Losses less than 12 Months, Gross Unrealized Losses	574	4,466
Losses more than 12 Months, Estimated Fair Value	10,143	61,506
Losses more than 12 Months, Gross Unrealized Losses	367	$ 588
Obligations of States and Municipal Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	22,495
Losses less than 12 Months, Gross Unrealized Losses	$ 381