Accumulated Other Comprehensive Loss - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 3,350,454	$ 2,533,165
Other comprehensive (loss) income before reclassifications	15,885
Amounts reclassified from other comprehensive (loss) income	289	1,680
Total other comprehensive income (loss)	16,174	(17,557)
Ending balance	3,444,879	3,245,003
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(33,559)
Other comprehensive (loss) income before reclassifications	16,267
Amounts reclassified from other comprehensive (loss) income	26
Total other comprehensive income (loss)	16,293
Ending balance	(17,266)
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,031)
Other comprehensive (loss) income before reclassifications	(382)
Amounts reclassified from other comprehensive (loss) income	208
Total other comprehensive income (loss)	(174)
Ending balance	(4,205)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(31,841)
Other comprehensive (loss) income before reclassifications	0
Amounts reclassified from other comprehensive (loss) income	55	112
Total other comprehensive income (loss)	55
Ending balance	(31,786)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(69,431)	(46,005)
Ending balance	$ (53,257)	$ (64,103)