Investment Securities - Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	$ 5,794,693	$ 4,996,970
Gross Unrealized Gains	182,063	241,999
Gross Unrealized Losses	(35,066)	(3,378)
Securities available-for-sale	5,941,690	5,235,591
Government agency and government-sponsored enterprise pass through securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	1,227,960	1,207,676
Gross Unrealized Gains	51,944	74,238
Gross Unrealized Losses	(6,502)	(37)
Securities available-for-sale	1,273,402	1,281,877
Government agency and government-sponsored enterprise collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	1,073,402	1,172,166
Gross Unrealized Gains	38,771	47,994
Gross Unrealized Losses	(3,345)	(280)
Securities available-for-sale	1,108,828	1,219,880
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	1,589,855	1,438,004
Gross Unrealized Gains	65,063	93,631
Gross Unrealized Losses	(8,864)	(18)
Securities available-for-sale	1,646,054	1,531,617
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	422,955	329,488
Gross Unrealized Gains	12,337	12,483
Gross Unrealized Losses	(2,192)	(897)
Securities available-for-sale	433,100	341,074
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	222,709	248,739
Gross Unrealized Gains	1,848	1,534
Gross Unrealized Losses	(542)	(770)
Securities available-for-sale	224,015	249,503
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	244,946	136,777
Gross Unrealized Gains	204	23
Gross Unrealized Losses	(910)	(924)
Securities available-for-sale	244,240	135,876
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	98,958	110,891
Gross Unrealized Gains	4,728	6,076
Gross Unrealized Losses	(310)	(21)
Securities available-for-sale	103,376	116,946
SBA asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	35,726	39,437
Gross Unrealized Gains	1,218	2,217
Gross Unrealized Losses	(34)	(27)
Securities available-for-sale	36,910	41,627
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	377,280	308,803
Gross Unrealized Gains	5,674	3,490
Gross Unrealized Losses	(2,547)	(404)
Securities available-for-sale	380,407	311,889
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	500,902	4,989
Gross Unrealized Gains	276	313
Gross Unrealized Losses	(9,820)	0
Securities available-for-sale	$ 491,358	$ 5,302