Fair Value Measurements (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Securities available‑for‑sale		$ (4,009,431)	$ (3,774,431)
Fair Value, Estimate Not Practicable, Equity Method Investments		4,891
Warrants Not Settleable in Cash, Fair Value Disclosure			5,161
Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(4,009,431)	(3,774,431)
Derivative Asset, Fair Value of Collateral		3,292	1,873
Warrants Not Settleable in Cash, Fair Value Disclosure		4,793	5,161
Assets, Fair Value Disclosure, Recurring		4,022,407	3,781,465
Derivative Liability, Fair Value of Collateral		142	1,379
Level 1
Securities available‑for‑sale			(5,922)
Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(403,405)	(5,922)
Derivative Asset, Fair Value of Collateral		0	0
Fair Value, Estimate Not Practicable, Equity Method Investments		4,891
Warrants Not Settleable in Cash, Fair Value Disclosure		0	0
Assets, Fair Value Disclosure, Recurring		408,296	5,922
Derivative Liability, Fair Value of Collateral		0	0
Level 2
Securities available‑for‑sale			(3,703,526)
Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(3,558,793)	(3,703,526)
Derivative Asset, Fair Value of Collateral		3,292	1,873
Fair Value, Estimate Not Practicable, Equity Method Investments		0
Warrants Not Settleable in Cash, Fair Value Disclosure		0	0
Assets, Fair Value Disclosure, Recurring		3,562,085	3,705,399
Derivative Liability, Fair Value of Collateral		142	1,379
Level 3
Securities available‑for‑sale			(64,983)
Warrants Not Settleable in Cash, Fair Value Disclosure			5,161		$ 5,497	$ 4,914
Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(47,233)	(64,983)
Derivative Asset, Fair Value of Collateral		0	0
Fair Value, Estimate Not Practicable, Equity Method Investments		0
Warrants Not Settleable in Cash, Fair Value Disclosure		4,793	5,161
Assets, Fair Value Disclosure, Recurring		52,026	70,144
Derivative Liability, Fair Value of Collateral		0	0
Government agency and government-sponsored enterprise pass through securities [Member]
Securities available‑for‑sale		(281,088)	(246,274)
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(281,088)	(246,274)
Government agency and government-sponsored enterprise pass through securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Government agency and government-sponsored enterprise pass through securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(281,088)	(246,274)
Government agency and government-sponsored enterprise pass through securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Securities available‑for‑sale		(632,850)	(275,709)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(632,850)	(275,709)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(632,850)	(275,709)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Private Label Collateralized Mortgage Obligations [Member]
Securities available‑for‑sale		(101,205)	(125,987)
Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(101,205)	(125,987)
Collateralized Mortgage Obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Collateralized Mortgage Obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(93,917)	(103,113)
Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(7,288)	(22,874)
Municipal Securities [Member]
Securities available‑for‑sale		(1,312,194)	(1,680,068)
Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(1,312,194)	(1,680,068)
Municipal Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Municipal Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(1,312,194)	(1,680,068)
Municipal Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Commercial Mortgage Backed Securities [Member]
Securities available‑for‑sale		(1,112,704)	(1,163,969)
Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(1,112,704)	(1,163,969)
Commercial Mortgage Backed Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Commercial Mortgage Backed Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(1,112,704)	(1,163,969)
Commercial Mortgage Backed Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
US Treasury Securities [Member]
Securities available‑for‑sale		(403,405)	0
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(403,405)
US Treasury Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(403,405)
US Treasury Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0
US Treasury Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0
Corporate Debt Securities [Member]
Securities available‑for‑sale		(17,553)	(19,295)
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(17,553)	(19,295)
Corporate Debt Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Corporate Debt Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(17,553)	(19,295)
Corporate Debt Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Collateralized Loan Obligations [Member]
Securities available‑for‑sale		0	(7,015)
Collateralized Loan Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale			(7,015)
Collateralized Loan Obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale			0
Collateralized Loan Obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale			(7,015)
Collateralized Loan Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale			0
SBA asset-backed securities [Member]
Securities available‑for‑sale		(67,047)	(160,334)
SBA asset-backed securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(67,047)	(160,334)
SBA asset-backed securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
SBA asset-backed securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(67,047)	(160,334)
SBA asset-backed securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Asset-backed Securities [Member]
Securities available‑for‑sale		(81,385)	(88,710)
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(81,385)	(88,710)
Asset-backed Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0	0
Asset-backed Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(41,440)	(46,601)
Asset-backed Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		(39,945)	(42,109)
Equity Securities [Member]
Securities available‑for‑sale	[1]	0	(7,070)	[2]
Equity Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	[2]		(5,922)
Equity Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	[2]		(1,148)
Equity Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	[2]		$ 0
Equity Securities [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 7,100

[1] In connection with our adoption of ASU 2016-01 and ASU 2018-03 on January 1, 2018, we reclassified $7.1 million of equity investments from securities available-for-sale to other assets in the first quarter of 2018. The reclassification was applied prospectively without prior period amounts being restated.

[2] In connection with our adoption of ASU 2016-01 and ASU 2018-03 on January 1, 2018, we reclassified $7.1 million of equity investments from securities available-for-sale to other assets in the first quarter of 2018. The reclassification was applied prospectively without prior period amounts being restated.