Loans and Allowance for Loan Losses, Based on Impairment Review Method (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	$ 0		$ 0
Collectively evaluated for impairment	50,155		49,595
Total ending allowance balance	50,155	$ 49,991	49,595	$ 48,144	$ 46,155	$ 44,317
Loans [Abstract]
Individually evaluated for impairment	20,053		21,581
Collectively evaluated for impairment	4,329,314		4,222,889
Total loans	4,349,367		4,244,470
Commercial [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	4,106		4,140
Total ending allowance balance	4,106	4,052	4,140	4,366	3,960	3,999
Loans [Abstract]
Individually evaluated for impairment	670		1,028
Collectively evaluated for impairment	213,494		211,464
Total loans	214,164		212,492
1 to 4 Family Residential Real Estate [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	45,617		44,950
Total ending allowance balance	45,617	45,507	44,950	43,274	41,643	39,748
Loans [Abstract]
Individually evaluated for impairment	19,383		20,553
Collectively evaluated for impairment	4,107,182		4,001,808
Total loans	4,126,565		4,022,361
Installment [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	432		505
Total ending allowance balance	432	$ 432	505	$ 504	$ 552	$ 570
Loans [Abstract]
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	8,638		9,617
Total loans	$ 8,638		$ 9,617