Securities - Summary Of Fair Value Of Available For Sale Securities By Contractual Maturities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	$ 10,533	$ 50,429
Due in one year or less, Fair value	10,557	50,659
Due after one year to five years, Amortized Cost	330,025	186,659
Due after one year to five years, Fair value	328,528	190,308
Due after five to ten years, Amortized Cost	1,486,171	759,068
Due after five to ten years, Fair value	1,476,228	763,869
Due after ten years, Amortized Cost	3,026,887	2,129,028
Due after ten years, Fair value	3,033,468	2,179,025
Amortized Cost	4,853,616	3,125,184
Available for sale securities	4,848,781	3,183,861
Government-sponsored residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
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	18,156	46,293
Due after one year to five years, Fair value	19,323	48,925
Due after five to ten years, Amortized Cost	593,853	96,338
Due after five to ten years, Fair value	597,546	100,278
Due after ten years, Amortized Cost	2,868,634	1,964,027
Due after ten years, Fair value	2,861,660	1,999,597
Amortized Cost	3,480,643	2,106,658
Available for sale securities	3,478,529	2,148,800
Government-sponsored commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
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	24,038	0
Due after one year to five years, Fair value	23,781	0
Due after five to ten years, Amortized Cost	159,024	17,054
Due after five to ten years, Fair value	158,014	17,081
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Amortized Cost	183,062	17,054
Available for sale securities	181,795	17,081
U.S. Agency bonds
Debt Securities, Available-for-sale [Line Items]
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	199,796	99,772
Due after one year to five years, Fair value	196,383	99,834
Due after five to ten years, Amortized Cost	660,779	570,696
Due after five to ten years, Fair value	644,622	566,875
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Amortized Cost	860,575	670,468
Available for sale securities	841,005	666,709
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	10,048	50,023
Due in one year or less, Fair value	10,071	50,251
Due after one year to five years, Amortized Cost	59,353	20,083
Due after one year to five years, Fair value	59,260	20,118
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	69,401	70,106
Available for sale securities	69,331	70,369
State and municipal bonds and obligations
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	485	406
Due in one year or less, Fair value	486	408
Due after one year to five years, Amortized Cost	28,682	20,511
Due after one year to five years, Fair value	29,781	21,431
Due after five to ten years, Amortized Cost	72,515	74,980
Due after five to ten years, Fair value	76,046	79,635
Due after ten years, Amortized Cost	158,253	165,001
Due after ten years, Fair value	171,808	179,428
Amortized Cost	259,935	260,898
Available for sale securities	$ 278,121	$ 280,902