Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 3,504,118	$ 3,277,312	$ 3,350,454	$ 2,533,165
Other comprehensive (loss) income before reclassifications	8,211		41,901
Amounts reclassified from other comprehensive (loss) income	452	642	1,062	3,095
Total other comprehensive income (loss)	8,663	(7,820)	42,963	(30,398)
Ending balance	3,558,075	3,302,936	3,558,075	3,302,936
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	1,214		(33,559)
Other comprehensive (loss) income before reclassifications	8,135		42,890
Amounts reclassified from other comprehensive (loss) income	72		90
Total other comprehensive income (loss)	8,207		42,980
Ending balance	9,421		9,421
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,614)		(4,031)
Other comprehensive (loss) income before reclassifications	76		(989)
Amounts reclassified from other comprehensive (loss) income	324		806
Total other comprehensive income (loss)	400		(183)
Ending balance	(4,214)		(4,214)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(31,731)		(31,841)
Other comprehensive (loss) income before reclassifications	0		0
Amounts reclassified from other comprehensive (loss) income	56	113	166	337
Total other comprehensive income (loss)	56		166
Ending balance	(31,675)		(31,675)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(35,131)	(69,124)	(69,431)	(46,005)
Ending balance	$ (26,468)	$ (76,944)	$ (26,468)	$ (76,944)