Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	$ 3,817,348	$ 4,009,431
Securities available-for-sale, at fair value	3,817,348	4,009,431
Equity Securities, FV-NI	4,715	4,891
Derivative Liability	1,446	142
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity warrants		4,793
Government agency and government-sponsored enterprise pass through securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	324,929	281,088
Government agency and government-sponsored enterprise collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,172,555	632,850
Private label collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	93,868	101,205
Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	113,874
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	721,981	1,312,194
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,100,017	1,112,704
US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	5,203	403,405
Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	214,151	81,385
SBA asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	49,746	67,047
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	21,024	17,553
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	3,817,348
Equity warrants	3,532	4,793
Other derivative assets	2,297	3,292
Total recurring assets	3,827,892	4,022,407
Derivative liabilities	1,446	142
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	5,203	403,405
Equity warrants	0	0
Other derivative assets	0	0
Equity Securities, FV-NI	4,715	4,891
Total recurring assets	9,918	408,296
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	3,774,182	3,558,793
Equity warrants	0	0
Other derivative assets	2,297	3,292
Equity Securities, FV-NI	0	0
Total recurring assets	3,776,479	3,562,085
Derivative liabilities	1,446	142
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	37,963	47,233
Equity warrants	3,532	4,793
Other derivative assets	0	0
Equity Securities, FV-NI	0	0
Total recurring assets	41,495	52,026
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	324,929	281,088
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	324,929	281,088
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,172,555	632,850
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,172,555	632,850
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Private label collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	93,868	101,205
Fair Value, Measurements, Recurring | Private label collateralized mortgage obligations | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Private label collateralized mortgage obligations | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	87,273	93,917
Fair Value, Measurements, Recurring | Private label collateralized mortgage obligations | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	6,595	7,288
Fair Value, Measurements, Recurring | Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	113,874
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	113,874
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0
Fair Value, Measurements, Recurring | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	721,981	1,312,194
Fair Value, Measurements, Recurring | Municipal securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Municipal securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	721,981	1,312,194
Fair Value, Measurements, Recurring | Municipal securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,100,017	1,112,704
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	1,100,017	1,112,704
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	5,203	403,405
Fair Value, Measurements, Recurring | US Treasury Securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	5,203	403,405
Fair Value, Measurements, Recurring | US Treasury Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | US Treasury Securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	214,151	81,385
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	182,783	41,440
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	31,368	39,945
Fair Value, Measurements, Recurring | SBA asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	49,746	67,047
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	49,746	67,047
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	21,024	17,553
Fair Value, Measurements, Recurring | Corporate debt securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Corporate debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	21,024	17,553
Fair Value, Measurements, Recurring | Corporate debt securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available‑for‑sale	$ 0	$ 0