Investment Securities - Gross unrealized losses (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Investment securities available-for-sale
Unrealized losses less than 12 months	$ (72,985)	$ (10,290)
Fair value less than 12 months	443,178	578,270
Unrealized losses over 12 months	(65,080)	(1,681)
Fair value over 12 months	281,967	55,084
Total Unrealized losses	(138,065)	(11,971)
Total Fair value	725,145	633,354
Held-to-maturity investment securities
Unrealized losses less than 12 months	(16,300)	(3,494)
Fair value less than 12 months	94,902	257,583
Unrealized losses over 12 months	(36,804)
Fair value over 12 months	178,404
Total Unrealized losses	(53,104)	(3,494)
Total Fair value	273,306	257,583
Unrealized losses less than 12 months	(89,285)	(13,784)
Fair value less than 12 months	538,080	835,853
Unrealized losses over 12 months	(101,884)	(1,681)
Fair value over 12 months	460,371	55,084
Total Unrealized losses	(191,169)	(15,465)
Total Fair value	998,451	890,937
U. S. Treasury and agencies
Investment securities available-for-sale
Unrealized losses less than 12 months	(19)
Fair value less than 12 months	529
Total Unrealized losses	(19)
Total Fair value	529
Mortgage backed securities - Residential agency
Investment securities available-for-sale
Unrealized losses less than 12 months	(60,983)	(10,156)
Fair value less than 12 months	325,016	554,811
Unrealized losses over 12 months	(63,204)	(1,681)
Fair value over 12 months	271,347	55,082
Total Unrealized losses	(124,187)	(11,837)
Total Fair value	596,363	609,893
Held-to-maturity investment securities
Unrealized losses less than 12 months		(3,145)
Fair value less than 12 months		204,373
Unrealized losses over 12 months	(34,268)
Fair value over 12 months	153,478
Total Unrealized losses	(34,268)	(3,145)
Total Fair value	153,478	204,373
Mortgage backed securities - Commercial
Investment securities available-for-sale
Unrealized losses less than 12 months	(5,425)	(123)
Fair value less than 12 months	54,666	17,470
Unrealized losses over 12 months	(1,876)
Fair value over 12 months	10,618
Total Unrealized losses	(7,301)	(123)
Total Fair value	65,284	17,470
Asset backed securities
Investment securities available-for-sale
Fair value less than 12 months	22
Fair value over 12 months	2	2
Total Fair value	24	2
Corporate bonds
Investment securities available-for-sale
Unrealized losses less than 12 months	(6,558)	(11)
Fair value less than 12 months	62,945	5,989
Total Unrealized losses	(6,558)	(11)
Total Fair value	62,945	5,989
Obligations of state and political agencies.
Held-to-maturity investment securities
Unrealized losses less than 12 months	(16,300)	(349)
Fair value less than 12 months	94,902	53,210
Unrealized losses over 12 months	(2,536)
Fair value over 12 months	24,926
Total Unrealized losses	(18,836)	(349)
Total Fair value	$ 119,828	$ 53,210