Investment Securities - Gross unrealized losses (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Investment securities available-for-sale
Unrealized losses less than 12 months	$ (58,556)	$ (10,290)
Fair value less than 12 months	569,144	578,270
Unrealized losses over 12 months	(36,395)	(1,681)
Fair value over 12 months	214,081	55,084
Total Unrealized losses	(94,951)	(11,971)
Total Fair value	783,225	633,354
Held-to-maturity investment securities
Unrealized losses less than 12 months	(37,794)	(3,494)
Fair value less than 12 months	290,506	257,583
Total Unrealized losses	(37,794)	(3,494)
Total Fair value	290,506	257,583
Unrealized losses less than 12 months	(96,350)	(13,784)
Fair value less than 12 months	859,650	835,853
Unrealized losses over 12 months	(36,395)	(1,681)
Fair value over 12 months	214,081	55,084
Total Unrealized losses	(132,745)	(15,465)
Total Fair value	1,073,731	890,937
Obligations of state and political agencies.
Held-to-maturity investment securities
Unrealized losses less than 12 months	(12,927)	(349)
Fair value less than 12 months	122,734	53,210
Total Unrealized losses	(12,927)	(349)
Total Fair value	122,734	53,210
Mortgage backed securities - Residential agency
Investment securities available-for-sale
Unrealized losses less than 12 months	(51,859)	(10,156)
Fair value less than 12 months	436,234	554,811
Unrealized losses over 12 months	(36,395)	(1,681)
Fair value over 12 months	214,079	55,082
Total Unrealized losses	(88,254)	(11,837)
Total Fair value	650,313	609,893
Held-to-maturity investment securities
Unrealized losses less than 12 months	(24,867)	(3,145)
Fair value less than 12 months	167,772	204,373
Total Unrealized losses	(24,867)	(3,145)
Total Fair value	167,772	204,373
Mortgage backed securities - Commercial
Investment securities available-for-sale
Unrealized losses less than 12 months	(3,947)	(123)
Fair value less than 12 months	76,130	17,470
Total Unrealized losses	(3,947)	(123)
Total Fair value	76,130	17,470
Asset backed securities
Investment securities available-for-sale
Fair value over 12 months	2	2
Total Fair value	2	2
Corporate bonds
Investment securities available-for-sale
Unrealized losses less than 12 months	(2,750)	(11)
Fair value less than 12 months	56,780	5,989
Total Unrealized losses	(2,750)	(11)
Total Fair value	$ 56,780	$ 5,989