Securities - Fair value of securities available for sale and related unrealized gain and loss (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	$ 1,440,831	$ 1,498,626
Unrealized Gains	3,060	3,989
Unrealized Losses	(218,672)	(172,134)
Fair Value	1,225,219	1,330,481
U.S. Government agencies
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	104,753	110,226
Unrealized Gains	4	24
Unrealized Losses	(14,824)	(11,777)
Fair Value	89,933	98,473
Mortgage Backed Securities - residential
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	669,417	711,131
Unrealized Gains	2	133
Unrealized Losses	(112,729)	(91,016)
Fair Value	556,690	620,248
Mortgage Backed Securities - commercial
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	7,958	10,103
Unrealized Losses	(674)	(426)
Fair Value	7,284	9,677
Collateralized Mortgage Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	214,507	228,344
Unrealized Gains		60
Unrealized Losses	(33,551)	(24,919)
Fair Value	180,956	203,485
State and municipal obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	402,144	396,522
Unrealized Gains	30	745
Unrealized Losses	(49,621)	(37,114)
Fair Value	352,553	360,153
Municipal taxable
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	39,875	39,321
Unrealized Gains		41
Unrealized Losses	(7,247)	(6,847)
Fair Value	32,628	32,515
U.S. Treasury
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	2,177	2,979
Unrealized Losses	(26)	(35)
Fair Value	2,151	2,944
Collateralized debt obligations
Amortized cost and fair value of investments classified as available for sale
Unrealized Gains	3,024	2,986
Fair Value	$ 3,024	$ 2,986