Securities - Summary of Amortized Cost and Fair Values of Securities Available-for-sale (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 1,478,635	$ 1,183,404
Available-for-sale Securities, Gross Unrealized Gains	32,937	7,593
Available-for-sale Securities, Gross Unrealized Losses	(2,361)	(4,705)
Available-for-sale Securities, Fair Value	1,509,211	1,186,292
U.S. Treasury Notes
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	25,456	41,403
Available-for-sale Securities, Gross Unrealized Gains	495	427
Available-for-sale Securities, Fair Value	25,951	41,830
U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	104,253	165,162
Available-for-sale Securities, Gross Unrealized Gains	814	542
Available-for-sale Securities, Gross Unrealized Losses	(357)	(754)
Available-for-sale Securities, Fair Value	104,710	164,950
Obligations of States, Municipalities, and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	103,895	92,806
Available-for-sale Securities, Gross Unrealized Gains	4,417	2,075
Available-for-sale Securities, Gross Unrealized Losses		(49)
Available-for-sale Securities, Fair Value	108,312	94,832
Agency, Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	807,798	490,427
Available-for-sale Securities, Gross Unrealized Gains	16,594	2,163
Available-for-sale Securities, Gross Unrealized Losses	(355)	(2,354)
Available-for-sale Securities, Fair Value	824,037	490,236
Non-Agency, Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	62,775	109,501
Available-for-sale Securities, Gross Unrealized Gains	1,321	593
Available-for-sale Securities, Gross Unrealized Losses		(272)
Available-for-sale Securities, Fair Value	64,096	109,822
Agency, Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	256,830	159,650
Available-for-sale Securities, Gross Unrealized Gains	7,415	1,092
Available-for-sale Securities, Gross Unrealized Losses	(513)	(1,041)
Available-for-sale Securities, Fair Value	263,732	159,701
Non-Agency, Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	11,215	31,144
Available-for-sale Securities, Gross Unrealized Gains	428	130
Available-for-sale Securities, Fair Value	11,643	31,274
Corporate Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	56,059	48,796
Available-for-sale Securities, Gross Unrealized Gains	1,364	571
Available-for-sale Securities, Gross Unrealized Losses	(215)	(37)
Available-for-sale Securities, Fair Value	57,208	49,330
Asset-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	50,354	44,515
Available-for-sale Securities, Gross Unrealized Gains	89
Available-for-sale Securities, Gross Unrealized Losses	(921)	(198)
Available-for-sale Securities, Fair Value	$ 49,522	$ 44,317

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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