Securities - Fair Value of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Available for sale
Amortized Cost	$ 1,090,363	$ 822,089
Gross Unrealized Gains	43,985	15,961
Gross Unrealized Losses	(323)	(3,274)
Fair Value	1,134,025	834,776
Held to maturity
Amortized Cost	168,676	207,899
Gross Unrealized Gains	11,314	7,336
Gross Unrealized Losses	0	(88)
Fair Value	179,990	215,147
U.S. Treasury and federal agencies
Available for sale
Amortized Cost	19,750	1,415
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(35)	(2)
Fair Value	19,715	1,413
State and municipal
Available for sale
Amortized Cost	803,100	396,931
Gross Unrealized Gains	35,014	11,288
Gross Unrealized Losses	(271)	(2,451)
Fair Value	837,843	405,768
Held to maturity
Amortized Cost	157,421	190,767
Gross Unrealized Gains	11,035	7,129
Gross Unrealized Losses	0	(54)
Fair Value	168,456	197,842
Federal agency collateralized mortgage obligations
Available for sale
Amortized Cost	144,022	267,272
Gross Unrealized Gains	3,448	2,543
Gross Unrealized Losses	(17)	(563)
Fair Value	147,453	269,252
Held to maturity
Amortized Cost	2,661	4,560
Gross Unrealized Gains	36	13
Gross Unrealized Losses	0	(5)
Fair Value	2,697	4,568
Federal agency mortgage–backed pools
Available for sale
Amortized Cost	114,484	145,623
Gross Unrealized Gains	4,315	1,207
Gross Unrealized Losses	0	(258)
Fair Value	118,799	146,572
Held to maturity
Amortized Cost	8,594	12,572
Gross Unrealized Gains	243	194
Gross Unrealized Losses	0	(29)
Fair Value	8,837	12,737
Corporate notes
Available for sale
Amortized Cost	9,007	10,848
Gross Unrealized Gains	1,208	923
Gross Unrealized Losses		0
Fair Value	$ 10,215	$ 11,771

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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