Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Securities Financing Transaction [Line Items]
Available-for-sale, amortized cost	$ 265,891	$ 180,154
Available-for-sale, gross unrealized gains	2,668	3,154
Available-for-sale, gross unrealized losses	(48)	(6)
Available-for-sale, estimated fair value	268,511	183,302
Allowance for Credit Losses	0	0
Held-to-maturity, amortized cost	1,087,209	942,314
Held-to-maturity, gross unrealized gains	21,294	29,378
Held-to-maturity, gross unrealized losses	(8,758)	(3,226)
Securities held-to-maturity, net encumbered	1,099,745	968,466
Allowance for Credit Losses	(1,717)	(1,715)
Total, amortized cost	1,353,100	1,122,468
Total, gross unrealized gains	23,962	32,532
Total, gross unrealized losses	(8,806)	(3,232)
Total, estimated fair value	1,368,256	1,151,768
Other
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	32,269
U.S. government and agency obligations | Securities investment
Securities Financing Transaction [Line Items]
Available-for-sale, amortized cost	169,337	173,790
Available-for-sale, gross unrealized gains	2,570	3,152
Available-for-sale, gross unrealized losses	(8)	(2)
Available-for-sale, estimated fair value	171,899	176,940
Allowance for Credit Losses	0	0
Collateralized loan obligations (“CLOs”) | Securities investment
Securities Financing Transaction [Line Items]
Available-for-sale, amortized cost	96,410	6,174
Available-for-sale, gross unrealized gains	96	0
Available-for-sale, gross unrealized losses	(40)	(4)
Available-for-sale, estimated fair value	96,466	6,170
Allowance for Credit Losses	0	0
State, municipal and sovereign debt obligations | Securities investment
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	278,179	238,405
Held-to-maturity, gross unrealized gains	7,043	11,500
Held-to-maturity, gross unrealized losses	(1,106)	(231)
Securities held-to-maturity, net encumbered	284,116	249,674
Allowance for Credit Losses	(90)	(48)
Corporate debt securities | Securities investment
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	72,821	72,305
Held-to-maturity, gross unrealized gains	1,542	1,615
Held-to-maturity, gross unrealized losses	(1,912)	(2,652)
Securities held-to-maturity, net encumbered	72,451	71,268
Allowance for Credit Losses	(1,511)	(1,550)
Mortgage-backed securities - FNMA
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	736,209	631,604
Held-to-maturity, gross unrealized gains	12,709	16,263
Held-to-maturity, gross unrealized losses	(5,740)	(343)
Securities held-to-maturity, net encumbered	743,178	647,524
Allowance for Credit Losses	(116)	(117)
Mortgage-backed securities - FNMA | FHLMC
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	303,539	232,942
Held-to-maturity, gross unrealized gains	4,256	5,383
Held-to-maturity, gross unrealized losses	(3,178)	(124)
Securities held-to-maturity, net encumbered	304,617	238,201
Allowance for Credit Losses	0
Mortgage-backed securities - FNMA | FNMA
Securities Financing Transaction [Line Items]
Available-for-sale, amortized cost	144	190
Available-for-sale, gross unrealized gains	2	2
Available-for-sale, gross unrealized losses	0	0
Available-for-sale, estimated fair value	146	192
Allowance for Credit Losses	0	0
Held-to-maturity, amortized cost	335,307	293,615
Held-to-maturity, gross unrealized gains	5,978	7,640
Held-to-maturity, gross unrealized losses	(2,481)	(147)
Securities held-to-maturity, net encumbered	338,804	301,108
Allowance for Credit Losses	0
Mortgage-backed securities - FNMA | GNMA
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	59,904	67,334
Held-to-maturity, gross unrealized gains	1,614	2,014
Held-to-maturity, gross unrealized losses	(23)	(12)
Securities held-to-maturity, net encumbered	61,495	69,336
Allowance for Credit Losses	0
Mortgage-backed securities - FNMA | SBA
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	5,190	5,392
Held-to-maturity, gross unrealized gains	0	0
Held-to-maturity, gross unrealized losses	(58)	(60)
Securities held-to-maturity, net encumbered	5,132	5,332
Allowance for Credit Losses	0
Mortgage-backed securities - FNMA | Other
Securities Financing Transaction [Line Items]
Held-to-maturity, amortized cost	32,269	32,321
Held-to-maturity, gross unrealized gains	861	1,226
Held-to-maturity, gross unrealized losses	0	0
Securities held-to-maturity, net encumbered	33,130	33,547
Allowance for Credit Losses	$ (116)	$ (117)