Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 62,108	$ 65,633	$ 178,550	$ 150,310
Other Comprehensive Income (Loss), net of tax:
Unrealized gain (loss) on securities	18,029	(12,531)	63,244	(46,806)
Reclassification adjustment for securities gains included in net income	(3,498)	(11)	(3,686)	(30)
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	3,430	791	5,425	791
Non-credit related unrealized (loss) gain on other-than-temporarily impaired debt securities	0	0	(682)	232
Amortization of net unrecognized pension and postretirement income	277	369	843	1,248
Other Comprehensive Income (Loss)	18,238	(11,382)	65,144	(44,565)
Total Comprehensive Income	$ 80,346	$ 54,251	$ 243,694	$ 105,745