Stockholders' Equity (Changes in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Unrealized gains on investment securities available for sale:
Net unrealized holding gain (loss) arising during the period, Before Tax	$ 252,893	$ 31,736	$ (33,743)	$ 61,147
Amounts reclassified to gain on investment securities available for sale, net, Before Tax	(5,723)	(3,914)	(7,253)	(8,231)
Net change in unrealized gains on securities available for sale, Before Tax	247,170	27,822	(40,996)	52,916
Net unrealized holding gain (loss) arising during the period, Tax Effect	(64,488)	(8,410)	8,988	(16,204)
Amounts reclassified to gain on investment securities available for sale, net, Tax Effect	1,459	1,037	1,849	2,181
Net change in unrealized gains on securities available for sale, Tax Effect	(63,029)	(7,373)	10,837	(14,023)
Net unrealized holding gain (loss) arising during the period, Net of Tax	188,405	23,326	(24,755)	44,943
Amounts reclassified to gain on investment securities available for sale, net, Net of Tax	(4,264)	(2,877)	(5,404)	(6,050)
Net change in unrealized gain (loss) on securities available for sale	184,141	20,449	(30,159)	38,893
Unrealized losses on derivative instruments:
Net unrealized holding gain (loss) arising during the period, Before Tax	(12,288)	(50,637)	(122,239)	(78,766)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	10,009	(1,688)	14,565	(4,411)
Net unrealized holding gain (loss) arising during the period, Tax Effect	1,218	13,419	30,355	20,873
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	(2,507)	447	(3,714)	1,169
Net unrealized holding gain (loss) arising during the period, Net of Tax	(11,070)	(37,218)	(91,884)	(57,893)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	7,502	(1,241)	10,851	(3,242)
Net change in unrealized losses on derivative instruments	(3,568)	(38,459)	(81,033)	(61,135)
Other comprehensive income (loss), Before Tax	244,891	(24,503)	(148,670)	(30,261)
Other comprehensive income (loss), Tax Effect	(64,318)	6,493	37,478	8,019
Other comprehensive income (loss)	180,573	(18,010)	(111,192)	(22,242)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	(2,279)	(52,325)	(107,674)	(83,177)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	$ (1,289)	$ 13,866	$ 26,641	$ 22,042