Securities - Schedule of Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized Cost And Fair Value Debt Securities [Abstract]
Total available-for-sale debt securities, Amortized Cost, Less than one year	$ 37,142
Total available-for-sale debt securities, Amortized Cost, 1-5 years	166,935
Total available-for-sale debt securities, Amortized Cost, 5-10 years	358,680
Total available-for-sale debt securities, Amortized Cost, Over 10 years	2,365,738
Available-for-sale, Amortized Cost	2,928,495	$ 1,916,658
Total held-to-maturity debt securities, Amortized Cost, Less than one year	11,599
Total held-to-maturity debt securities, Amortized Cost, 1-5 years	133,817
Total held-to-maturity debt securities, Amortized Cost, 5-10 years	225,448
Total held-to-maturity debt securities, Amortized Cost, Over 10 years	531,308
Held-to-maturity, Amortized Cost	902,172	731,212
Total debt securities, Amortized Cost	3,830,667
Total available-for-sale debt securities, Fair Value, Less than one year	37,211
Total available-for-sale debt securities, Fair Value, 1-5 years	175,090
Total available-for-sale debt securities, Fair Value, 5-10 years	366,224
Total available-for-sale debt securities, Fair Value, Over 10 years	2,385,739
Total available-for-sale debt securities, Fair Value	2,964,264	1,978,136
Total held-to-maturity debt securities, Fair Value, Less than one year	11,711
Total held-to-maturity debt securities, Fair Value, 1-5 years	140,934
Total held-to-maturity debt securities, Fair Value, 5-10 years	235,791
Total held-to-maturity debt securities, Fair Value, Over 10 years	546,051
Total held-to-maturity debt securities, Fair Value	934,487	768,183
Total debt securities, Fair Value	$ 3,898,751	$ 2,746,319