Loans Held-for-Investment and Allowance for Loan Losses - Schedule of Company's Internal Ratings of its Loans Held-for-Investment, Including The Year of Origination, by Portfolio Segments (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	$ 711,000	$ 2,585,000	$ 754,000
2021-2020	2,363,000	1,027,000	2,070,000
2020-2019	885,000	499,000	729,000
2019-2018	427,000	353,000	510,000
2018-2017	319,000	236,000	321,000
Prior	743,000	579,000	837,000
Revolving Loans Amortized Cost Basis	118,000	110,000	102,000
Total	5,566,000	5,389,000	5,323,000
C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	166,000	537,000	306,000
2021-2020	449,000	183,000	656,000
2020-2019	124,000	57,000	86,000
2019-2018	47,000	32,000	64,000
2018-2017	26,000	17,000	26,000
Prior	26,000	11,000	41,000
Total	838,000	837,000	1,179,000
Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	25,000	39,000	2,000
2021-2020	33,000	15,000	23,000
2020-2019	15,000	6,000	16,000
2019-2018	5,000	22,000	23,000
2018-2017	21,000	17,000	19,000
Prior	93,000	79,000	94,000
Total	192,000	178,000	177,000
Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	20,000	73,000	16,000
2021-2020	51,000	9,000	47,000
2020-2019	6,000	6,000	16,000
2019-2018	4,000	6,000	7,000
2018-2017	1,000	3,000	3,000
Prior	1,000	1	1,000
Total	83,000	98,000	90,000
Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	119,000	561,000	102,000
2021-2020	532,000	136,000	352,000
2020-2019	107,000	24,000	67,000
2019-2018	22,000	14,000	35,000
2018-2017	13,000	7,000	17,000
Prior	13,000	8,000	15,000
Total	806,000	750,000	588,000
Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	25,000	118,000	20,000
2021-2020	110,000	43,000	61,000
2020-2019	40,000	15,000	22,000
2019-2018	13,000	11,000	18,000
2018-2017	9,000	7,000	10,000
Prior	29,000	23,000	31,000
Total	226,000	217,000	162,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	52,000	214,000	45,000
2021-2020	211,000	130,000	199,000
2020-2019	129,000	92,000	120,000
2019-2018	76,000	57,000	87,000
2018-2017	54,000	41,000	51,000
Prior	114,000	90,000	148,000
Total	636,000	624,000	650,000
Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	102,000	260,000	75,000
2021-2020	263,000	147,000	176,000
2020-2019	140,000	118,000	134,000
2019-2018	97,000	103,000	114,000
2018-2017	101,000	65,000	80,000
Prior	178,000	129,000	181,000
Total	881,000	822,000	760,000
Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	108,000	483,000	110,000
2021-2020	448,000	237,000	354,000
2020-2019	215,000	118,000	160,000
2019-2018	108,000	87,000	124,000
2018-2017	81,000	71,000	96,000
Prior	281,000	235,000	316,000
Revolving Loans Amortized Cost Basis	111,000	103,000	95,000
Total	1,352,000	1,334,000	1,255,000
Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	68,000	219,000	61,000
2021-2020	197,000	105,000	162,000
2020-2019	90,000	55,000	91,000
2019-2018	45,000	17,000	32,000
2018-2017	14,000	7,000	16,000
Prior	6,000	2,000	8,000
Total	420,000	405,000	370,000
Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	26,000	81,000	17,000
2021-2020	69,000	22,000	40,000
2020-2019	19,000	8,000	17,000
2019-2018	6,000	4,000	6,000
2018-2017	3,000	1,000	3,000
Prior	2,000	1,000	2,000
Revolving Loans Amortized Cost Basis	7,000	7,000	7,000
Total	132,000	124,000	92,000
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	704,000	2,548,000	747,000
2021-2020	2,327,000	1,005,000	2,024,000
2020-2019	862,000	471,000	694,000
2019-2018	400,000	332,000	482,000
2018-2017	302,000	217,000	291,000
Prior	702,000	548,000	794,000
Revolving Loans Amortized Cost Basis	116,000	107,000	101,000
Total	5,413,000	5,228,000	5,133,000
Pass [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	163,000	526,000	303,000
2021-2020	438,000	178,000	647,000
2020-2019	121,000	52,000	84,000
2019-2018	42,000	29,000	61,000
2018-2017	24,000	17,000	24,000
Prior	26,000	11,000	41,000
Total	814,000	813,000	1,160,000
Pass [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	25,000	39,000	2,000
2021-2020	33,000	15,000	21,000
2020-2019	15,000	6,000	16,000
2019-2018	5,000	22,000	23,000
2018-2017	21,000	17,000	13,000
Prior	93,000	79,000	92,000
Total	192,000	178,000	167,000
Pass [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	20,000	69,000	15,000
2021-2020	47,000	8,000	42,000
2020-2019	6,000	6,000	16,000
2019-2018	4,000	6,000	7,000
2018-2017	1,000	3,000	2,000
Prior	1,000	1	1,000
Total	79,000	93,000	83,000
Pass [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	118,000	557,000	101,000
2021-2020	524,000	134,000	347,000
2020-2019	106,000	24,000	62,000
2019-2018	21,000	14,000	35,000
2018-2017	13,000	7,000	17,000
Prior	13,000	8,000	13,000
Total	795,000	744,000	575,000
Pass [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	25,000	117,000	20,000
2021-2020	110,000	42,000	54,000
2020-2019	39,000	15,000	21,000
2019-2018	13,000	10,000	17,000
2018-2017	8,000	7,000	10,000
Prior	28,000	23,000	30,000
Total	223,000	214,000	152,000
Pass [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	52,000	214,000	45,000
2021-2020	211,000	128,000	198,000
2020-2019	123,000	77,000	105,000
2019-2018	62,000	56,000	86,000
2018-2017	52,000	31,000	41,000
Prior	101,000	84,000	136,000
Total	601,000	590,000	611,000
Pass [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	100,000	250,000	74,000
2021-2020	258,000	143,000	168,000
2020-2019	136,000	114,000	126,000
2019-2018	88,000	90,000	96,000
2018-2017	97,000	59,000	72,000
Prior	166,000	117,000	169,000
Total	845,000	773,000	705,000
Pass [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	107,000	477,000	109,000
2021-2020	441,000	230,000	346,000
2020-2019	208,000	115,000	157,000
2019-2018	106,000	84,000	119,000
2018-2017	78,000	68,000	93,000
Prior	266,000	222,000	302,000
Revolving Loans Amortized Cost Basis	109,000	100,000	94,000
Total	1,315,000	1,296,000	1,220,000
Pass [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	68,000	218,000	61,000
2021-2020	197,000	105,000	161,000
2020-2019	89,000	54,000	90,000
2019-2018	44,000	17,000	32,000
2018-2017	14,000	7,000	16,000
Prior	6,000	2,000	8,000
Total	418,000	403,000	368,000
Pass [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	26,000	81,000	17,000
2021-2020	68,000	22,000	40,000
2020-2019	19,000	8,000	17,000
2019-2018	6,000	4,000	6,000
2018-2017	3,000	1,000	3,000
Prior	2,000	1,000	2,000
Revolving Loans Amortized Cost Basis	7,000	7,000	7,000
Total	131,000	124,000	92,000
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		12,000	3,000
2021-2020	10,000	8,000	12,000
2020-2019	7,000	17,000	23,000
2019-2018	15,000	1,000	2,000
2018-2017	2,000	9,000	14,000
Prior	13,000	7,000	8,000
Revolving Loans Amortized Cost Basis	1,000	1
Total	48,000	55,000	62,000
Special Mention [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		4,000	2,000
2021-2020	4,000	1,000	3,000
2020-2019		4,000	1,000
2019-2018	3,000
2018-2017			1,000
Total	7,000	9,000	7,000
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021			1,000
Total			1,000
Special Mention [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		2,000
2021-2020	2,000		2,000
2020-2019			4,000
Prior			1,000
Total	2,000	2,000	7,000
Special Mention [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021-2020		1,000	1,000
2020-2019	1,000	12,000	13,000
2019-2018	11,000		1,000
2018-2017	1,000	7,000	8,000
Prior	8,000	3	4,000
Total	21,000	23,000	27,000
Special Mention [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		2,000
2021-2020	1,000	2,000	3,000
2020-2019	2,000	1,000	4,000
2018-2017	1,000	1,000	4,000
Prior	1,000	1,000
Total	5,000	7,000	11,000
Special Mention [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		3,000
2021-2020	3,000	4,000	3,000
2020-2019	4,000		1,000
2019-2018		1,000	1,000
2018-2017	1,000	1,000	1,000
Prior	4,000	3,000	3,000
Revolving Loans Amortized Cost Basis	1,000	1
Total	13,000	13,000	9,000
Special Mention [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		1
Total		1
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	7,000	25,000	4,000
2021-2020	26,000	14,000	34,000
2020-2019	16,000	11,000	12,000
2019-2018	12,000	20,000	26,000
2018-2017	15,000	10,000	16,000
Prior	28,000	24,000	35,000
Revolving Loans Amortized Cost Basis	1,000	2,000	1,000
Total	105,000	106,000	128,000
Substandard [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	3,000	7,000	1,000
2021-2020	7,000	4,000	6,000
2020-2019	3,000	1,000	1,000
2019-2018	2,000	3,000	3,000
2018-2017	2,000		1,000
Total	17,000	15,000	12,000
Substandard [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021-2020			2,000
2018-2017			6,000
Prior			2,000
Total			10,000
Substandard [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		4,000
2021-2020	4,000	1	5,000
2018-2017			1,000
Total	4,000	5,000	6,000
Substandard [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	1,000	2,000	1,000
2021-2020	6,000	2,000	3,000
2020-2019	1,000		1,000
2019-2018	1
Prior			1,000
Total	9,000	4,000	6,000
Substandard [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021		1,000
2021-2020		1,000	7,000
2020-2019	1,000		1,000
2019-2018		1,000	1,000
2018-2017	1,000
Prior	1,000		1,000
Total	3,000	3,000	10,000
Substandard [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021-2020		1,000
2020-2019	5,000	3,000	2,000
2019-2018	3,000	1,000
2018-2017	1,000	3,000	2,000
Prior	5,000	3,000	8,000
Total	14,000	11,000	12,000
Substandard [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	2,000	8,000	1,000
2021-2020	4,000	2,000	5,000
2020-2019	2,000	3,000	4,000
2019-2018	3,000	13,000	18,000
2018-2017	9,000	5,000	4,000
Prior	11,000	11,000	12,000
Total	31,000	42,000	44,000
Substandard [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022-2021	1,000	3,000	1,000
2021-2020	4,000	3,000	5,000
2020-2019	3,000	3,000	2,000
2019-2018	2,000	2,000	4,000
2018-2017	2,000	2,000	2,000
Prior	11,000	10,000	11,000
Revolving Loans Amortized Cost Basis	1,000	2,000	1,000
Total	24,000	25,000	26,000
Substandard [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021-2020			1,000
2020-2019	1,000	1,000	1,000
2019-2018	1,000
Total	2,000	$ 1,000	$ 2,000
Substandard [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021-2020	1,000
Total	$ 1,000