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Securities, Held to Maturity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	$ 616,560	$ 630,074
Unrealized gains	21,942	11,817
Unrealized losses	1,675	629
Estimated fair value	636,827	641,262
Allowance for credit losses on HTM securities	0
Transactions of HTM securities [Abstract]
Gains from calls on HTM securities	24	12	$ 0
Held-to-maturity securities sold, amortized cost	1,000	0	$ 0
Held-to-maturity securities sold, realized loss	1
Federal Agency [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	100,000
Unrealized gains	0
Unrealized losses	1,658
Estimated fair value	98,342
Mortgage-backed Securities, Government-Sponsored Enterprises [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	107,914	149,448
Unrealized gains	4,583	3,184
Unrealized losses	0	155
Estimated fair value	112,497	152,477
Mortgage-Backed, U.S. Government Agency Securities [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	11,533	13,667
Unrealized gains	979	584
Unrealized losses	0	0
Estimated fair value	12,512	14,251
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	103,105	189,402
Unrealized gains	4,477	2,165
Unrealized losses	0	368
Estimated fair value	107,582	191,199
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	79,145	110,498
Unrealized gains	3,950	3,256
Unrealized losses	0	100
Estimated fair value	83,095	113,654
State & Municipal [Member]
Held-to-maturity securities, fair value to amortized cost [Abstract]
Amortized cost	214,863	167,059
Unrealized gains	7,953	2,628
Unrealized losses	17	6
Estimated fair value	222,799	169,681
Public Deposits and Other Purposes [Member]
Securities pledged [Abstract]
Amortized costs of securities available for sale and held to maturity pledged	1,400,000	1,300,000
Securities Sold under Repurchase Agreements [Member]
Securities pledged [Abstract]
Amortized costs of securities available for sale and held to maturity pledged	$ 305,200	$ 189,800

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Amount of realized loss on investment in debt security measured at amortized cost (held-to-maturity), which was sold during the period.

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