Securities - Summary Of Fair Value Of Securities By Contractual Maturities (Detail) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Available for sale securities
Due in one year or less, Amortized Cost	$ 14,960,000	$ 51,955,000
Due in one year or less, Fair value	14,908,000	51,932,000
Due after one year to five years, Amortized Cost	877,833,000	784,326,000
Due after one year to five years, Fair value	825,369,000	773,349,000
Due after five to ten years, Amortized Cost	2,123,184,000	2,023,620,000
Due after five to ten years, Fair value	1,994,305,000	1,994,423,000
Due after ten years, Amortized Cost	5,440,643,000	5,727,278,000
Due after ten years, Fair value	5,082,723,000	5,691,520,000
Amortized Cost	8,456,620,000	8,587,179,000
Fair Value	7,917,305,000	8,511,224,000
Held to maturity securities
Due in one year or less, Amortized Cost	0
Due in one year or less, Fair value	0
Due after one year to five years, Amortized Cost	0
Due after one year to five years, Fair value	0
Due after five to ten years, Amortized Cost	203,203,000
Due after five to ten years, Fair value	203,210,000
Due after ten years, Amortized Cost	192,231,000
Due after ten years, Fair value	188,913,000
Amortized Cost	395,434,000
Fair Value	392,123,000	0
Total
Due in one year or less, Amortized Cost	14,960,000
Due in one year or less, Fair value	14,908,000
Due after one year to five years, Amortized Cost	877,833,000
Due after one year to five years, Fair value	825,369,000
Due after five to ten years, Amortized Cost	2,326,387,000
Due after five to ten years, Fair value	2,197,515,000
Due after ten years, Amortized Cost	5,632,874,000
Due after ten years, Fair value	5,271,636,000
Amortized Cost	8,852,054,000
Fair Value	8,309,428,000
Government-sponsored residential mortgage-backed securities
Available for sale securities
Due in one year or less, Amortized Cost	1,000	0
Due in one year or less, Fair value	1,000	0
Due after one year to five years, Amortized Cost	20,992,000	24,935,000
Due after one year to five years, Fair value	21,143,000	25,962,000
Due after five to ten years, Amortized Cost	832,510,000	899,169,000
Due after five to ten years, Fair value	790,125,000	892,029,000
Due after ten years, Amortized Cost	4,476,245,000	4,653,188,000
Due after ten years, Fair value	4,158,077,000	4,606,717,000
Amortized Cost	5,329,748,000	5,577,292,000
Fair Value	4,969,346,000	5,524,708,000
Held to maturity securities
Due in one year or less, Amortized Cost	0
Due in one year or less, Fair value	0
Due after one year to five years, Amortized Cost	0
Due after one year to five years, Fair value	0
Due after five to ten years, Amortized Cost	0
Due after five to ten years, Fair value	0
Due after ten years, Amortized Cost	192,231,000
Due after ten years, Fair value	188,913,000
Amortized Cost	192,231,000
Fair Value	188,913,000
Government-sponsored commercial mortgage-backed securities
Available for sale securities
Due in one year or less, Amortized Cost	0	0
Due in one year or less, Fair value	0	0
Due after one year to five years, Amortized Cost	190,509,000	139,095,000
Due after one year to five years, Fair value	182,639,000	137,755,000
Due after five to ten years, Amortized Cost	700,994,000	387,177,000
Due after five to ten years, Fair value	658,732,000	378,414,000
Due after ten years, Amortized Cost	815,628,000	894,476,000
Due after ten years, Fair value	774,556,000	892,699,000
Amortized Cost	1,707,131,000	1,420,748,000
Fair Value	1,615,927,000	1,408,868,000
Held to maturity securities
Due in one year or less, Amortized Cost	0
Due in one year or less, Fair value	0
Due after one year to five years, Amortized Cost	0
Due after one year to five years, Fair value	0
Due after five to ten years, Amortized Cost	203,203,000
Due after five to ten years, Fair value	203,210,000
Due after ten years, Amortized Cost	0
Due after ten years, Fair value	0
Amortized Cost	203,203,000
Fair Value	203,210,000
U.S. Agency bonds
Available for sale securities
Due in one year or less, Amortized Cost	0	5,508,000
Due in one year or less, Fair value	0	5,515,000
Due after one year to five years, Amortized Cost	578,810,000	531,821,000
Due after one year to five years, Fair value	537,301,000	520,935,000
Due after five to ten years, Amortized Cost	521,106,000	665,048,000
Due after five to ten years, Fair value	476,598,000	648,564,000
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Amortized Cost	1,099,916,000	1,202,377,000
Fair Value	1,013,899,000	1,175,014,000
U.S. Treasury securities
Available for sale securities
Due in one year or less, Amortized Cost	10,000,000	40,010,000
Due in one year or less, Fair value	9,955,000	40,001,000
Due after one year to five years, Amortized Cost	49,458,000	49,424,000
Due after one year to five years, Fair value	46,280,000	48,604,000
Due after five to ten years, Amortized Cost	0	0
Due after five to ten years, Fair value	0	0
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Amortized Cost	59,458,000	89,434,000
Fair Value	56,235,000	88,605,000
State and municipal bonds and obligations
Available for sale securities
Due in one year or less, Amortized Cost	4,659,000	6,137,000
Due in one year or less, Fair value	4,653,000	6,116,000
Due after one year to five years, Amortized Cost	36,766,000	33,692,000
Due after one year to five years, Fair value	36,723,000	34,704,000
Due after five to ten years, Amortized Cost	68,574,000	72,226,000
Due after five to ten years, Fair value	68,850,000	75,416,000
Due after ten years, Amortized Cost	148,770,000	151,855,000
Due after ten years, Fair value	150,090,000	164,093,000
Amortized Cost	258,769,000	263,910,000
Fair Value	260,316,000	280,329,000
Small Business Administration pooled securities
Available for sale securities
Due in one year or less, Amortized Cost		0
Due in one year or less, Fair value		0
Due after one year to five years, Amortized Cost		4,062,000
Due after one year to five years, Fair value		4,092,000
Due after five to ten years, Amortized Cost		0
Due after five to ten years, Fair value		0
Due after ten years, Amortized Cost		27,759,000
Due after ten years, Fair value		28,011,000
Amortized Cost		31,821,000
Fair Value		32,103,000
Other debt securities
Available for sale securities
Due in one year or less, Amortized Cost	300,000	300,000
Due in one year or less, Fair value	299,000	300,000
Due after one year to five years, Amortized Cost	1,298,000	1,297,000
Due after one year to five years, Fair value	1,283,000	1,297,000
Due after five to ten years, Amortized Cost	0	0
Due after five to ten years, Fair value	0	0
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Amortized Cost	1,598,000	1,597,000
Fair Value	$ 1,582,000	$ 1,597,000