Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 35,197	$ 45,467	$ 84,677	$ 88,847
Other Comprehensive (Loss) Income, net of tax:
Unrealized (loss) gain on securities	(6,631)	10,268	(34,275)	14,541
Reclassification adjustment for securities gains included in net income	(3)	(932)	(19)	(1,651)
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	(8)	0	(232)	0
Amortization of net unrecognized pension and postretirement items	540	341	879	684
Other Comprehensive (Loss) Income	(6,086)	9,677	(33,183)	13,574
Total Comprehensive Income	$ 29,111	$ 55,144	$ 51,494	$ 102,421