Securities - Schedule of Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost And Fair Value Debt Securities [Abstract]
Total available-for-sale debt securities, Amortized Cost, Less than one year	$ 60,162
Total available-for-sale debt securities, Amortized Cost, 1-5 years	145,702
Total available-for-sale debt securities, Amortized Cost, 5-10 years	409,137
Total available-for-sale debt securities, Amortized Cost, Over 10 years	1,754,415
Available-for-sale, Amortized Cost	2,369,416	$ 2,142,056
Total held-to-maturity debt securities, Amortized Cost, Less than one year	20,968
Total held-to-maturity debt securities, Amortized Cost, 1-5 years	124,311
Total held-to-maturity debt securities, Amortized Cost, 5-10 years	316,440
Total held-to-maturity debt securities, Amortized Cost, Over 10 years	390,034
Held-to-maturity, Amortized Cost	851,753	1,020,934
Total debt securities, Amortized Cost	3,221,169
Total available-for-sale debt securities, Fair Value, Less than one year	60,188
Total available-for-sale debt securities, Fair Value, 1-5 years	147,933
Total available-for-sale debt securities, Fair Value, 5-10 years	415,068
Total available-for-sale debt securities, Fair Value, Over 10 years	1,770,369
Total available-for-sale debt securities, Fair Value	2,393,558	2,114,129
Total held-to-maturity debt securities, Fair Value, Less than one year	21,040
Total held-to-maturity debt securities, Fair Value, 1-5 years	128,105
Total held-to-maturity debt securities, Fair Value, 5-10 years	325,593
Total held-to-maturity debt securities, Fair Value, Over 10 years	399,785
Total held-to-maturity debt securities, Fair Value	874,523	1,020,743
Total debt securities, Fair Value	$ 3,268,081	$ 3,134,872