Investment Securities - Unrealized Losses on Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	$ 488,734	$ 716,081
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(4,318)	(3,545)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	164,983	1,756
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(3,940)	(10)
Unrealized Losses on Securities Available-for-Sale, Fair Value	653,717	717,837
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(8,258)	(3,555)
Government agency and government-sponsored enterprise pass through securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	3,066	0
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(4)	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	9,241	186
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(50)	(1)
Unrealized Losses on Securities Available-for-Sale, Fair Value	12,307	186
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(54)	(1)
Government agency and government-sponsored enterprise collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	77,168	180,071
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(263)	(572)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0	1,456
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0	(7)
Unrealized Losses on Securities Available-for-Sale, Fair Value	77,168	181,527
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(263)	(579)
Municipal securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	189,163	38,667
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(1,539)	(339)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	189,163	38,667
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(1,539)	(339)
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	1,753	214,862
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(33)	(537)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	1,753	214,862
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(33)	(537)
Asset-backed Securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	44,658	165,575
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(339)	(1,670)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	122,729	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(2,193)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	167,387	165,575
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(2,532)	(1,670)
Collateralized loan obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	102,396	102,469
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(1,938)	(403)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	32,937	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(1,695)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	135,333	102,469
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(3,633)	(403)
Private label collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	8,510	9,872
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(26)	(11)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	76	114
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(2)	(2)
Unrealized Losses on Securities Available-for-Sale, Fair Value	8,586	9,986
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(28)	(13)
SBA asset-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	1,964	4,565
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(25)	(13)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	1,964	4,565
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(25)	$ (13)
Corporate debt securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	60,056
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(151)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	60,056
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	$ (151)