Securities - Summary Of Fair Value Of Available For Sale Securities By Contractual Maturities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	$ 10,470	$ 50,429
Due in one year or less, Fair value	10,501	50,659
Due after one year to five years, Amortized Cost	228,941	186,659
Due after one year to five years, Fair value	228,874	190,308
Due after five to ten years, Amortized Cost	1,015,714	759,068
Due after five to ten years, Fair value	993,478	763,869
Due after ten years, Amortized Cost	2,768,594	2,129,028
Due after ten years, Fair value	2,753,400	2,179,025
Total Amortized Cost	4,023,719	3,125,184
Available for sale securities	3,986,253	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	20,503	46,293
Due after one year to five years, Fair value	21,777	48,925
Due after five to ten years, Amortized Cost	87,383	96,338
Due after five to ten years, Fair value	91,340	100,278
Due after ten years, Amortized Cost	2,606,012	1,964,027
Due after ten years, Fair value	2,578,585	1,999,597
Total Amortized Cost	2,713,898	2,106,658
Available for sale securities	2,691,702	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	24,090	0
Due after one year to five years, Fair value	23,771	0
Due after five to ten years, Amortized Cost	94,974	17,054
Due after five to ten years, Fair value	92,500	17,081
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Total Amortized Cost	119,064	17,054
Available for sale securities	116,271	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	99,784	99,772
Due after one year to five years, Fair value	98,111	99,834
Due after five to ten years, Amortized Cost	760,770	570,696
Due after five to ten years, Fair value	733,561	566,875
Due after ten years, Amortized Cost	0	0
Due after ten years, Fair value	0	0
Total Amortized Cost	860,554	670,468
Available for sale securities	831,672	666,709
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	10,065	50,023
Due in one year or less, Fair value	10,095	50,251
Due after one year to five years, Amortized Cost	59,320	20,083
Due after one year to five years, Fair value	58,995	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
Total Amortized Cost	69,385	70,106
Available for sale securities	69,090	70,369
State and municipal bonds and obligations
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, Amortized Cost	405	406
Due in one year or less, Fair value	406	408
Due after one year to five years, Amortized Cost	25,244	20,511
Due after one year to five years, Fair value	26,220	21,431
Due after five to ten years, Amortized Cost	72,587	74,980
Due after five to ten years, Fair value	76,077	79,635
Due after ten years, Amortized Cost	162,582	165,001
Due after ten years, Fair value	174,815	179,428
Total Amortized Cost	260,818	260,898
Available for sale securities	$ 277,518	$ 280,902