Stockholders' Equity and EPS - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	$ 167,078	$ 46,055
Related tax benefit	(187,315)	(49,357)
Net interest income	659,579	524,137
Total reclassification adjustment for gains included in net income, net of tax	532,220	132,253
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassification adjustment for gains included in net income, net of tax	(11,305)	(45,722)
Accumulated Net Investment Gain (Loss) Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	0	(61,165)
Related tax benefit	0	(16,953)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Related tax benefit	(4,352)	(579)
Net interest income	$ (15,657)	$ (2,089)