Investment Securities Held-to-Maturity - Summary of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,653,986	$ 1,438,903
Gross Unrealized Gains	6,014	9,781
Gross Unrealized Losses	24,192	9,724
Estimated Fair Value	1,635,808	1,438,960
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	148,326	186,734
Gross Unrealized Gains	1,066	2,234
Gross Unrealized Losses	527	141
Estimated Fair Value	148,865	188,827
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	46,140
Gross Unrealized Losses	1,088
Estimated Fair Value	45,052
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,459,520	1,252,169
Gross Unrealized Gains	4,948	7,547
Gross Unrealized Losses	22,577	9,583
Estimated Fair Value	$ 1,441,891	$ 1,250,133