Investment Securities - Unrealized Losses on Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	$ 307,867	$ 716,081
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(8,066)	(3,545)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	70,787	1,756
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(4,108)	(10)
Unrealized Losses on Securities Available-for-Sale, Fair Value	378,654	717,837
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(12,174)	(3,555)
Government agency and government-sponsored enterprise pass through securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	9,281	0
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(52)	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	0	186
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	0	(1)
Unrealized Losses on Securities Available-for-Sale, Fair Value	9,281	186
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(52)	(1)
Government agency and government-sponsored enterprise collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	0	180,071
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	0	(572)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	1,308	1,456
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(9)	(7)
Unrealized Losses on Securities Available-for-Sale, Fair Value	1,308	181,527
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(9)	(579)
Municipal securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	20,448	38,667
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(84)	(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	20,448	38,667
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(84)	(339)
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	2,403	214,862
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(47)	(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	2,403	214,862
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(47)	(537)
Asset-backed Securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	116,863	165,575
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(3,400)	(1,670)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	36,800	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(2,031)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	153,663	165,575
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(5,431)	(1,670)
Collateralized loan obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	104,062	102,469
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(3,352)	(403)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	32,601	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(2,065)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	136,663	102,469
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(5,417)	(403)
Private label collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	52,839	9,872
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(1,096)	(11)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	78	114
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(3)	(2)
Unrealized Losses on Securities Available-for-Sale, Fair Value	52,917	9,986
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(1,099)	(13)
SBA asset-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	1,971	4,565
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(35)	(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	1,971	4,565
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	$ (35)	$ (13)