Securities - Schedule of Securities Classified as Available-for-Sale with Gross Unrealized Losses Aggregated by Category and Length of Time (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	$ 360,275	$ 310,452
Losses less than 12 Months, Gross Unrealized Losses	5,548	1,521
Losses more than 12 Months, Estimated Fair Value	638,003	418,361
Losses more than 12 Months, Gross Unrealized Losses	30,369	14,501
U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Losses more than 12 Months, Estimated Fair Value	96,785	96,844
Losses more than 12 Months, Gross Unrealized Losses	3,628	3,731
Obligations of U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	25,978	1,577
Losses less than 12 Months, Gross Unrealized Losses	183	9
Losses more than 12 Months, Estimated Fair Value	10,152	14,323
Losses more than 12 Months, Gross Unrealized Losses	101	57
MBS
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	259,794	306,274
Losses less than 12 Months, Gross Unrealized Losses	2,864	1,490
Losses more than 12 Months, Estimated Fair Value	405,974	172,324
Losses more than 12 Months, Gross Unrealized Losses	16,029	7,044
Obligations of States and Municipal Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Losses less than 12 Months, Estimated Fair Value	74,503	2,601
Losses less than 12 Months, Gross Unrealized Losses	2,501	22
Losses more than 12 Months, Estimated Fair Value	125,092	134,870
Losses more than 12 Months, Gross Unrealized Losses	$ 10,611	$ 3,669