Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Securities available‑for‑sale	$ (5,235,591)	$ (3,797,187)
Equity Securities, FV-NI	6,147	2,998
Alternative Investment	32,300
Fair Value, Recurring
Securities available‑for‑sale	(5,235,591)
Warrants Not Settleable in Cash, Fair Value Disclosure	4,520	3,434
Derivative Liability, Fair Value of Collateral	1,150	755
Level 1 | Fair Value, Recurring
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Derivative Liability, Fair Value of Collateral	0	0
Equity Securities, FV-NI	6,147	2,998
Level 2 | Fair Value, Recurring
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Derivative Liability, Fair Value of Collateral	1,150	755
Equity Securities, FV-NI	0	0
Level 3
Warrants Not Settleable in Cash, Fair Value Disclosure		3,434	$ 4,793	$ 5,161
Level 3 | Fair Value, Recurring
Warrants Not Settleable in Cash, Fair Value Disclosure	4,520	3,434
Derivative Liability, Fair Value of Collateral	0	0
Equity Securities, FV-NI	0	0
Government agency and government-sponsored enterprise pass through securities [Member]
Securities available‑for‑sale	(1,281,877)	(1,108,224)
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(341,074)	(305,198)
Government agency and government-sponsored enterprise pass through securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise pass through securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(341,074)	(305,198)
Government agency and government-sponsored enterprise pass through securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Securities available‑for‑sale	(1,219,880)	(1,136,397)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(1,219,880)	(1,136,397)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(1,219,880)	(1,136,397)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Private Label Collateralized Mortgage Obligations [Member]
Securities available‑for‑sale	(116,946)	(99,483)
Private Label Collateralized Mortgage Obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(116,946)	(99,483)
Private Label Collateralized Mortgage Obligations [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Private Label Collateralized Mortgage Obligations [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(112,299)	(93,219)
Private Label Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	(4,647)	(6,264)
Municipal Securities [Member]
Securities available‑for‑sale	(1,531,617)	(735,159)
Municipal Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(1,531,617)	(735,159)
Municipal Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Municipal Securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(1,531,617)	(735,159)
Municipal Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(1,281,877)	(1,108,224)
Commercial Mortgage Backed Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Commercial Mortgage Backed Securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(1,281,877)	(1,108,224)
Commercial Mortgage Backed Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
US Treasury Securities [Member]
Securities available‑for‑sale	(5,302)	(5,181)
US Treasury Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(5,302)	(5,181)
US Treasury Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	(5,302)	(5,181)
US Treasury Securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	0	0
US Treasury Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Corporate Debt Securities [Member]
Securities available‑for‑sale	(311,889)	(20,748)
Corporate Debt Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(311,889)	(20,748)
Corporate Debt Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Corporate Debt Securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(311,889)	(20,748)
Corporate Debt Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Collateralized Loan Obligations [Member]
Securities available‑for‑sale	(135,876)	(123,756)
Collateralized Loan Obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(135,876)	(123,756)
Collateralized Loan Obligations [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Collateralized Loan Obligations [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(135,876)	(123,756)
Collateralized Loan Obligations [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
SBA asset-backed securities [Member]
Securities available‑for‑sale	(41,627)	(48,258)
SBA asset-backed securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(41,627)	(48,258)
SBA asset-backed securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
SBA asset-backed securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(41,627)	(48,258)
SBA asset-backed securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Asset-backed Securities [Member]
Securities available‑for‑sale	(249,503)	(214,783)
Asset-backed Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(249,503)	(214,783)
Asset-backed Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Asset-backed Securities [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(223,778)	(198,348)
Asset-backed Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	$ (25,725)	$ (16,435)