Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 4,384,188	$ 3,350,454
Other comprehensive (loss) income before reclassifications	25,011
Amounts reclassified from other comprehensive (loss) income	637	289
Total other comprehensive income	25,648	16,174
Ending balance	4,420,998	3,444,879
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	5,822
Other comprehensive (loss) income before reclassifications	26,068
Amounts reclassified from other comprehensive (loss) income	27
Total other comprehensive income	26,095
Ending balance	31,917
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(3,729)
Other comprehensive (loss) income before reclassifications	(1,057)
Amounts reclassified from other comprehensive (loss) income	438
Total other comprehensive income	(619)
Ending balance	(4,348)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(34,307)
Other comprehensive (loss) income before reclassifications	0
Amounts reclassified from other comprehensive (loss) income	172	55
Total other comprehensive income	172
Ending balance	(34,135)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(32,214)	(69,431)
Ending balance	$ (6,566)	$ (53,257)