Investment Securities - Gross unrealized losses (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Investment securities available-for-sale
Unrealized losses less than 12 months	$ (2,450)	$ (19,761)
Fair value less than 12 months	22,873	178,719
Unrealized losses over 12 months	(124,881)	(112,503)
Fair value over 12 months	679,981	535,024
Total Unrealized losses	(127,331)	(132,264)
Total Fair value	702,854	713,743
Held-to-maturity investment securities
Unrealized losses less than 12 months		(3,336)
Fair value less than 12 months		18,788
Unrealized losses over 12 months		(47,654)
Fair value over 12 months		249,623
Total Unrealized losses		(50,990)
Total Fair value		268,411
Unrealized losses less than 12 months		(23,097)
Fair value less than 12 months		197,507
Unrealized losses over 12 months		(160,157)
Fair value over 12 months		784,647
Total Unrealized losses		(183,254)
Total Fair value		982,154
U. S. Treasury and agencies
Investment securities available-for-sale
Unrealized losses less than 12 months	(12)	(17)
Fair value less than 12 months	427	509
Total Unrealized losses	(12)	(17)
Total Fair value	427	509
Mortgage backed securities - Residential agency
Investment securities available-for-sale
Unrealized losses less than 12 months	(63)	(10,457)
Fair value less than 12 months	2,575	79,693
Unrealized losses over 12 months	(109,653)	(107,711)
Fair value over 12 months	578,913	507,418
Total Unrealized losses	(109,716)	(118,168)
Total Fair value	581,488	587,111
Held-to-maturity investment securities
Unrealized losses over 12 months		(33,254)
Fair value over 12 months		150,861
Total Unrealized losses		(33,254)
Total Fair value		150,861
Mortgage backed securities - Commercial
Investment securities available-for-sale
Unrealized losses less than 12 months	(300)	(4,835)
Fair value less than 12 months	4,941	50,437
Unrealized losses over 12 months	(5,940)	(2,276)
Fair value over 12 months	57,830	13,120
Total Unrealized losses	(6,240)	(7,111)
Total Fair value	62,771	63,557
Asset backed securities
Investment securities available-for-sale
Fair value less than 12 months	30	32
Fair value over 12 months	2	2
Total Fair value	32	34
Corporate bonds
Investment securities available-for-sale
Unrealized losses less than 12 months	(2,075)	(4,452)
Fair value less than 12 months	14,900	48,048
Unrealized losses over 12 months	(9,288)	(2,516)
Fair value over 12 months	43,236	14,484
Total Unrealized losses	(11,363)	(6,968)
Total Fair value	$ 58,136	62,532
Obligations of state and political agencies.
Held-to-maturity investment securities
Unrealized losses less than 12 months		(3,336)
Fair value less than 12 months		18,788
Unrealized losses over 12 months		(14,400)
Fair value over 12 months		98,762
Total Unrealized losses		(17,736)
Total Fair value		$ 117,550