Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 4,474,488	$ 3,504,118	$ 4,384,188	$ 3,350,454
Other comprehensive (loss) income before reclassification	(1,179)		25,565
Amounts reclassified from other comprehensive income	1,334	452	1,866	1,062
Total other comprehensive income	155	8,663	27,431	42,963
Ending balance	4,533,763	3,558,075	4,533,763	3,558,075
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	34,961		5,822
Other comprehensive (loss) income before reclassification	(1,262)		27,819
Amounts reclassified from other comprehensive income	36		94
Total other comprehensive income	(1,226)		27,913
Ending balance	33,735		33,735
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(5,936)		(3,729)
Other comprehensive (loss) income before reclassification	83		(2,254)
Amounts reclassified from other comprehensive income	1,127		1,257
Total other comprehensive income	1,210		(997)
Ending balance	(4,726)		(4,726)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(33,963)		(34,307)
Other comprehensive (loss) income before reclassification	0		0
Amounts reclassified from other comprehensive income	171	56	515	166
Total other comprehensive income	171		515
Ending balance	(33,792)		(33,792)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,938)	(35,131)	(32,214)	(69,431)
Ending balance	$ (4,783)	$ (26,468)	$ (4,783)	$ (26,468)