Investment Securities - Unrealized Losses on Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	$ 1,734,185	$ 457,559
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(34,223)	(2,474)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	96,552	90,077
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(843)	(904)
Unrealized Losses on Securities Available-for-Sale, Fair Value	1,830,737	547,636
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(35,066)	(3,378)
Government agency and government-sponsored enterprise pass through securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	177,833	90,722
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(6,502)	(897)
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	177,833	90,722
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(6,502)	(897)
Government agency and government-sponsored enterprise collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	148,694	97,863
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(3,345)	(280)
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	148,694	97,863
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(3,345)	(280)
Municipal securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	446,081	5,919
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(8,864)	(18)
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	446,081	5,919
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(8,864)	(18)
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	186,057	58,408
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(2,172)	(37)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	1,330	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(20)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	187,387	58,408
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(2,192)	(37)
Asset-backed Securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	27,843	17,694
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(72)	(63)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	44,246	61,031
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(470)	(707)
Unrealized Losses on Securities Available-for-Sale, Fair Value	72,089	78,725
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(542)	(770)
Collateralized loan obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	82,027	96,442
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(593)	(729)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	48,694	28,972
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(317)	(195)
Unrealized Losses on Securities Available-for-Sale, Fair Value	130,721	125,414
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(910)	(924)
Private label collateralized mortgage obligations
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	29,344	788
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(308)	(19)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	365	74
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	29,709	862
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(310)	(21)
SBA asset-backed securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	0	2,127
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	0	(27)
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Fair Value	1,917	0
Unrealized Losses on Securities Available-for-Sale, 12 Months or Longer, Gross Unrealized Losses	(34)	0
Unrealized Losses on Securities Available-for-Sale, Fair Value	1,917	2,127
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(34)	(27)
Corporate debt securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	150,214	87,596
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(2,547)	(404)
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	150,214	87,596
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	(2,547)	$ (404)
U.S. Treasury securities
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Fair Value	486,092
Unrealized Losses on Securities Available-for-Sale, Less than 12 Months, Gross Unrealized Losses	(9,820)
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	486,092
Unrealized Losses on Securities Available-for-Sale, Gross Unrealized Losses	$ (9,820)