Securities - Fair Value of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available for sale
Amortized Cost	$ 976,813	$ 822,089
Gross Unrealized Gains	39,317	15,961
Gross Unrealized Losses	(787)	(3,274)
Fair Value	1,015,343	834,776
Held to maturity
Amortized Cost	180,270	207,899
Gross Unrealized Gains	11,342	7,336
Gross Unrealized Losses	0	(88)
Fair Value	191,612	215,147
U.S. Treasury and federal agencies
Available for sale
Amortized Cost	6,250	1,415
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(11)	(2)
Fair Value	6,239	1,413
State and municipal
Available for sale
Amortized Cost	651,256	396,931
Gross Unrealized Gains	27,978	11,288
Gross Unrealized Losses	(775)	(2,451)
Fair Value	678,459	405,768
Held to maturity
Amortized Cost	165,858	190,767
Gross Unrealized Gains	10,919	7,129
Gross Unrealized Losses	0	(54)
Fair Value	176,777	197,842
Federal agency collateralized mortgage obligations
Available for sale
Amortized Cost	180,628	267,272
Gross Unrealized Gains	5,222	2,543
Gross Unrealized Losses	(1)	(563)
Fair Value	185,849	269,252
Held to maturity
Amortized Cost	2,839	4,560
Gross Unrealized Gains	67	13
Gross Unrealized Losses	0	(5)
Fair Value	2,906	4,568
Federal agency mortgage-backed pools
Available for sale
Amortized Cost	127,802	145,623
Gross Unrealized Gains	4,670	1,207
Gross Unrealized Losses	0	(258)
Fair Value	132,472	146,572
Held to maturity
Amortized Cost	11,573	12,572
Gross Unrealized Gains	356	194
Gross Unrealized Losses	0	(29)
Fair Value	11,929	12,737
Corporate notes
Available for sale
Amortized Cost	10,877	10,848
Gross Unrealized Gains	1,447	923
Gross Unrealized Losses	0	0
Fair Value	$ 12,324	$ 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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