Stockholders' Equity and EPS - Reclassification of AOCI (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for losses on available-for-sale securities included in net income									$ 134,670,000	$ 88,094,000	$ 64,603,000
Related tax benefit	$ (94,061,000)	$ (105,075,000)	$ (119,114,000)	$ (107,435,000)	$ (105,000,000)	$ (95,308,000)	$ (77,287,000)	$ (73,966,000)	(425,685,000)	(351,561,000)	(355,463,000)
Net interest income	533,668,000	520,644,000	529,403,000	512,886,000	514,460,000	493,222,000	466,443,000	419,863,000	2,096,601,000	1,893,988,000	1,420,369,000
Net income available to common stockholders	$ 262,856,000	$ 267,281,000	$ 317,987,000	$ 288,732,000	$ 266,264,000	$ 274,817,000	$ 237,798,000	$ 194,961,000	1,136,856,000	973,840,000	490,506,000
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income available to common stockholders									6,687,000	535,000	3,091,000
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for losses on available-for-sale securities included in net income									3,905,000	740,000	5,189,000
Related tax benefit									(1,087,000)	(205,000)	(2,098,000)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Related tax benefit									(1,489,000)	0	0
Net interest income									$ 5,358,000	$ 0	$ 0