Investment Securities (Securities Available for Sale) (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,890,042	$ 1,901,798
Gross unrealized gains	1,947	2,159
Gross unrealized losses	(225,683)	(213,845)
Available for sale debt securities, at fair value	1,666,306	1,690,112
U.S. Treasury obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	276,863	276,618
Gross unrealized gains	0	0
Gross unrealized losses	(24,476)	(22,740)
Available for sale debt securities, at fair value	252,387	253,878
Agency-guaranteed obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	22,392	26,310
Gross unrealized gains	1,126	1,188
Gross unrealized losses	0	0
Available for sale debt securities, at fair value	23,518	27,498
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,446,173	1,462,159
Gross unrealized gains	119	377
Gross unrealized losses	(186,411)	(176,927)
Available for sale debt securities, at fair value	1,259,881	1,285,609
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	29,978	31,809
Gross unrealized gains	702	594
Gross unrealized losses	(163)	(168)
Available for sale debt securities, at fair value	30,517	32,235
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	64,211	64,454
Gross unrealized gains	0	0
Gross unrealized losses	(8,446)	(7,870)
Available for sale debt securities, at fair value	55,765	56,584
Corporate obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	50,425	40,448
Gross unrealized gains	0	0
Gross unrealized losses	(6,187)	(6,140)
Available for sale debt securities, at fair value	$ 44,238	$ 34,308