Securities - Schedule of Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost And Fair Value Debt Securities [Abstract]
Total available-for-sale debt securities, Amortized Cost, Within one year	$ 27,501
Total available-for-sale debt securities, Amortized Cost, After 1 year through 5 years	127,072
Total available-for-sale debt securities, Amortized Cost, After 5 years through 10 years	386,343
Total available-for-sale debt securities, Amortized Cost, After 10 years	2,048,153
Available-for-sale, Amortized Cost	2,589,069	$ 2,874,776
Total held-to-maturity debt securities, Amortized Cost, Within one year	18,814
Total held-to-maturity debt securities, Amortized Cost, After 1 year through 5 years	110,471
Total held-to-maturity debt securities, Amortized Cost, After 5 years through 10 years	464,698
Total held-to-maturity debt securities, Amortized Cost, After 10 years	617,009
Held-to-maturity, Amortized Cost	1,210,992	1,248,629
Total debt securities, Amortized Cost	3,800,061
Total available-for-sale debt securities, Fair Value, Within one year	26,969
Total available-for-sale debt securities, Fair Value, After 1 year through 5 years	122,529
Total available-for-sale debt securities, Fair Value, After 5 years through 10 years	360,145
Total available-for-sale debt securities, Fair Value, After 10 years	1,686,498
Total available-for-sale debt securities, Fair Value	2,196,141	2,529,140
Total held-to-maturity debt securities, Fair Value, Within one year	18,694
Total held-to-maturity debt securities, Fair Value, After 1 year through 5 years	106,721
Total held-to-maturity debt securities, Fair Value, After 5 years through 10 years	406,786
Total held-to-maturity debt securities, Fair Value, After 10 years	466,786
Total held-to-maturity debt securities, Fair Value	998,987	1,084,390
Total debt securities, Fair Value	$ 3,195,128	$ 3,613,530