Investment Securities Held-to-Maturity - Summary of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 2,351,120	$ 2,046,647
Gross Unrealized Gains	21,429	2,660
Gross Unrealized Losses	11,245	57,886
Estimated Fair Value	2,361,304	1,991,421
U.S. Treasury [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		9,960
Gross Unrealized Losses		2
Estimated Fair Value		9,958
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	98,867	234,228
Gross Unrealized Gains	527	336
Gross Unrealized Losses	96	803
Estimated Fair Value	99,298	233,761
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	44,379	52,051
Gross Unrealized Gains	182
Gross Unrealized Losses	303	2,065
Estimated Fair Value	44,258	49,986
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,207,874	1,750,408
Gross Unrealized Gains	20,720	2,324
Gross Unrealized Losses	10,846	55,016
Estimated Fair Value	$ 2,217,748	$ 1,697,716