Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Securities available‑for‑sale	$ (3,797,187)	$ (4,009,431)
Equity Securities, FV-NI	2,998	4,891
Fair Value, Recurring
Securities available‑for‑sale	(3,797,187)
Derivative Asset, Fair Value of Collateral	1,234	3,292
Warrants Not Settleable in Cash, Fair Value Disclosure	3,434	4,793
Derivative Liability, Fair Value of Collateral	755	142
Assets, Fair Value Disclosure	3,804,853	4,022,407
Level 1 | Fair Value, Recurring
Derivative Asset, Fair Value of Collateral	0	0
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Derivative Liability, Fair Value of Collateral	0	0
Equity Securities, FV-NI	2,998	4,891
Assets, Fair Value Disclosure	8,179	408,296
Level 2 | Fair Value, Recurring
Derivative Asset, Fair Value of Collateral	1,234	3,292
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Derivative Liability, Fair Value of Collateral	755	142
Equity Securities, FV-NI	0	0
Assets, Fair Value Disclosure	3,770,541	3,562,085
Level 3
Warrants Not Settleable in Cash, Fair Value Disclosure		4,793	$ 5,161	$ 5,497
Level 3 | Fair Value, Recurring
Derivative Asset, Fair Value of Collateral	0	0
Warrants Not Settleable in Cash, Fair Value Disclosure	3,434	4,793
Derivative Liability, Fair Value of Collateral	0	0
Equity Securities, FV-NI	0	0
Assets, Fair Value Disclosure	26,133	52,026
Government agency and government-sponsored enterprise pass through securities [Member]
Securities available‑for‑sale	(305,198)	(281,088)
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(305,198)	(281,088)
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	(305,198)	(281,088)
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	(1,136,397)	(632,850)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(1,136,397)	(632,850)
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	(1,136,397)	(632,850)
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	(99,483)	(101,205)
Private Label Collateralized Mortgage Obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(99,483)	(101,205)
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	(93,219)	(93,917)
Private Label Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	(6,264)	(7,288)
Municipal Securities [Member]
Securities available‑for‑sale	(735,159)	(1,312,194)
Municipal Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(735,159)	(1,312,194)
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	(735,159)	(1,312,194)
Municipal Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Commercial Mortgage Backed Securities [Member]
Securities available‑for‑sale	(1,108,224)	(1,112,704)
Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(1,108,224)	(1,112,704)
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	(1,108,224)	(1,112,704)
Commercial Mortgage Backed Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
US Treasury Securities [Member]
Securities available‑for‑sale	(5,181)	(403,405)
US Treasury Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(5,181)	(403,405)
US Treasury Securities [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	(5,181)	(403,405)
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	(20,748)	(17,553)
Corporate Debt Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(20,748)	(17,553)
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	(20,748)	(17,553)
Corporate Debt Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Collateralized Loan Obligations [Member]
Securities available‑for‑sale	(123,756)
Collateralized Loan Obligations [Member] | Fair Value, Recurring
Securities available‑for‑sale	(123,756)
Collateralized Loan Obligations [Member] | Level 1 | Fair Value, Recurring
Securities available‑for‑sale	0
Collateralized Loan Obligations [Member] | Level 2 | Fair Value, Recurring
Securities available‑for‑sale	(123,756)
Collateralized Loan Obligations [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0
SBA asset-backed securities [Member]
Securities available‑for‑sale	(48,258)	(67,047)
SBA asset-backed securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(48,258)	(67,047)
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	(48,258)	(67,047)
SBA asset-backed securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	0	0
Asset-backed Securities [Member]
Securities available‑for‑sale	(214,783)	(81,385)
Asset-backed Securities [Member] | Fair Value, Recurring
Securities available‑for‑sale	(214,783)	(81,385)
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	(198,348)	(41,440)
Asset-backed Securities [Member] | Level 3 | Fair Value, Recurring
Securities available‑for‑sale	$ (16,435)	$ (39,945)