Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	$ 3,631,566	$ 3,688,091
Gross Unrealized Gains	159,691	112,651
Gross Unrealized Losses	(33,594)	(3,555)
Securities available‑for‑sale	3,757,663	3,797,187
Government agency and government-sponsored enterprise pass through securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	1,068,810	1,083,182
Gross Unrealized Gains	57,997	25,579
Gross Unrealized Losses	(1,375)	(537)
Securities available‑for‑sale	1,125,432	1,108,224
Government agency and government-sponsored enterprise collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	1,069,657	1,112,573
Gross Unrealized Gains	40,124	24,403
Gross Unrealized Losses	(7,684)	(579)
Securities available‑for‑sale	1,102,097	1,136,397
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	687,603	691,647
Gross Unrealized Gains	46,310	43,851
Gross Unrealized Losses	(29)	(339)
Securities available‑for‑sale	733,884	735,159
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	277,213	294,606
Gross Unrealized Gains	12,733	10,593
Gross Unrealized Losses	(115)	(1)
Securities available‑for‑sale	289,831	305,198
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	220,624	216,133
Gross Unrealized Gains	41	320
Gross Unrealized Losses	(9,966)	(1,670)
Securities available‑for‑sale	210,699	214,783
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	142,144	124,134
Gross Unrealized Gains	0	25
Gross Unrealized Losses	(12,062)	(403)
Securities available‑for‑sale	130,082	123,756
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	99,021	96,066
Gross Unrealized Gains	1,096	3,430
Gross Unrealized Losses	(2,255)	(13)
Securities available‑for‑sale	97,862	99,483
SBA asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	44,508	47,765
Gross Unrealized Gains	998	506
Gross Unrealized Losses	(65)	(13)
Securities available‑for‑sale	45,441	48,258
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	17,000	17,000
Gross Unrealized Gains	0	3,748
Gross Unrealized Losses	(43)	0
Securities available‑for‑sale	16,957	20,748
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Total securities available-for-sale	4,986	4,985
Gross Unrealized Gains	392	196
Gross Unrealized Losses	0	0
Securities available‑for‑sale	$ 5,378	$ 5,181