Stockholders' Equity and EPS - Reclassification out of AOCI (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	$ 47,698,000	$ 36,114,000	$ 76,726,000	$ 45,172,000
Related tax benefit	(119,114,000)	(77,287,000)	(226,549,000)	(151,253,000)
Net interest income	529,403,000	466,443,000	1,042,289,000	886,306,000
Total reclassification adjustment for losses included in net income, net of tax	317,987,000	237,798,000	606,719,000	432,759,000
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassification adjustment for losses included in net income, net of tax	565,000	0	3,187,000	0
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	275,000	0	3,905,000	0
Related tax benefit	(77,000)	0	1,087,000	0
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	(141,000)	0	142,000	0
Net interest income	$ 508,000	$ 0	$ 511,000	$ 0