Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 3,444,879	$ 3,245,003	$ 3,350,454	$ 2,533,165
Other comprehensive (loss) income before reclassifications	17,805		33,690
Amounts reclassified from other comprehensive (loss) income	321	773	610	2,453
Total other comprehensive income (loss)	18,126	(5,021)	34,300	(22,578)
Ending balance	3,504,118	3,277,312	3,504,118	3,277,312
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(17,266)		(33,559)
Other comprehensive (loss) income before reclassifications	18,488		34,755
Amounts reclassified from other comprehensive (loss) income	(8)		18
Total other comprehensive income (loss)	18,480		34,773
Ending balance	1,214		1,214
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,205)		(4,031)
Other comprehensive (loss) income before reclassifications	(683)		(1,065)
Amounts reclassified from other comprehensive (loss) income	274		482
Total other comprehensive income (loss)	(409)		(583)
Ending balance	(4,614)		(4,614)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(31,786)		(31,841)
Other comprehensive (loss) income before reclassifications	0		0
Amounts reclassified from other comprehensive (loss) income	55	112	110	224
Total other comprehensive income (loss)	55		110
Ending balance	(31,731)		(31,731)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(53,257)	(64,103)	(69,431)	(46,005)
Ending balance	$ (35,131)	$ (69,124)	$ (35,131)	$ (69,124)